High-level Football Research Articles

Feature Extraction of Foul Action of Football Players Based on Machine Vision

With the improvement of technology and tactics, the rhythm of football match is getting faster and faster, which leads to more intense competition behavior in a football match; the physical contact of both players is also increasing, and the frequency of fouls by football players is getting higher and higher. This leads to fouls by players. Because of the error of visual analysis, in the crowd of high-level football players, the traditional football players’ foul behavior feature extraction method has the problem of low precision of foul action feature extraction. This paper mainly studies the feature extraction of soccer players’ foul action based on machine vision. To solve these problems, this paper uses a machine vision-based football player foul action feature extraction method, using a machine vision system to obtain football player action image, based on threshold recognition algorithm to identify the football player’s foul action. Based on the recognition of the foul action image, the potential function sequence of the foul action sequence is established by the Harris 3D operator, and the characteristic data of football player foul action are filtered by the AdaBoost algorithm. The simulation results show that this method has high accuracy in identifying fouls in the range of high-level football players and effectively reduces the recognition error. The method proposed in this paper can effectively analyze the characteristics of foul action and help football clubs to develop more perfect tactics.

Physical and Anthropometric Characteristics Do Not Differ According to Birth Year Quartile in High-Level Junior Australian Football Players.

The aim of this study was to explore differences in the physical fitness and anthropometric profiles between birth year quartiles of players attending the Australian Football League (AFL) National Draft Combine. Date of birth, anthropometric, 20 m sprint, vertical and running vertical jump, AFL planned agility, and 20 m Multi-Stage Fitness Test (MSFT) data were obtained for players selected to attend the Combine between 1999 and 2019 (n = 1549; Mage = 18.1; SDage = 0.3). The underlying density distributions of the data were visually explored using violin plots overlaid with box and whisker plots. A multivariate analysis of variance (MANOVA) was then used to model the main effect of birth quartile (four levels) on the physical and anthropometric scores. Results showed that physical and anthropometric test scores did not significantly differ according to birth quartile (V = 0.008, F = 0.880, p = 0.631). We conclude that the physical and anthropometric profiles of high-level junior Australian Football players were similar according to birth year quartile across the modeled period. Therefore, how players utilize their physical and anthropometric attributes during game-play via contextualized, representative assessments, such as small-sided games, should be considered when examining potential causes of a RAE.

Associations between maximal strength, sprint, and jump height and match physical performance in high-level female football players.

Studies on females' decisive physical components to physical match-play performance are sparse and only emphasize endurance tests. Thus, the influence of maximal strength and power on physical performance during match-play is currently unknown. The aim of this study was to assess the association between one repetition maximum (1RM) half squat strength, 5-, 10-, and 15-m sprint times, countermovement jump (CMJ) height, and physical high-intensity match-play performance in high-level female football players. Thirty-seven female high-level football players completed 1-2 football matches with physical performance measured by local positioning tracking. Correlations were assessed between physical match-play performance variables (total distance covered, running distance, high-intensity running distance, sprinting distance as well as acceleration and deceleration counts, and peak speed) and laboratory tests (half squat 1RM, 15-m sprint, and CMJ). We found no correlation between 1RM and physical match-play performance. Further, 10-m- and 15-m sprint time (r=-0.56, r=-0.56, p<0.001) and CMJ jump height (r=0.50, p<0.01) strongly correlated with peak match speed. Further, there was a moderate correlation between 15-m sprint time and ACC (r=-0.43, p<0.05). 5-m sprint time did not correlate with physical match-play performance. Laboratory-based sprint and jump performance, but not maximal half squat strength, showed moderate to large correlations with high-intensity physical match-play performance measures in high-level female football players.

Hamstring Strain Injury (HSI) Prevention in Professional and Semi-Professional Football Teams: A Systematic Review and Meta-Analysis.

Hamstring Strain Injuries (HSIs) are the most common type of lesion in professional footballers and the leading cause of absence days from sports. However, recent studies have shown that high-level football teams apparently do not apply any HSI prevention protocol. The aim of the study was to determine the effect of preventive strategies and protocols in reducing the incidence of hamstring muscle injuries in professional and semi-professional football teams. A literature search of PubMed/MEDLINE, ISI/Web of Science and Scopus databases was conducted with the keywords “hamstring* and (injury* or strain) and prevent* and (soccer or football)”. Quality and bias assessment was completed through the Kennelly modified scale. The Injury Incidence Rate (IIR) and the Incidence Rate Ratio (IRR) were assessed in the statistical analysis. In the meta-analysis, data were extracted, pooled and analysed with “Comprehensive Meta-Analysis Version 3.3.070” software. In total, 8 of the 1017 original search studies met the inclusion criteria of this review. The total exposure of the studies was 170,221.8 h, while the number of HSIs recorded was 165 in the intervention groups and 224 in the control groups. The average score of the quality assessment was 23.6/34. The meta-analysis of six of the eight included studies provided strong evidence that interventions are effective in reducing hamstring injuries. The IRR of the effect size was 0.443, with p-value = 0.001. The studies analysed applied different preventive strategies: the Nordic hamstring exercise, the FIFA 11+ programme and exercises for core stability or balance training. All these interventions proved to have a successful effect on prevention of hamstring injuries.

Observational Analysis of Corner Kicks in High-Level Football: A Mixed Methods Study

Corner kicks are one of the most important set pieces in high-level football. The present study aimed to analyze the evolution of the tactical approach to corner kicks in high-performance football. For this, a total of 1704 corner kicks executed in the 192 matches corresponding to the 2010, 2014 and 2018 FIFA World Cups were analyzed. To achieve the proposed objectives, the observational methodology was used. The results show an evolution in the mode of execution of these actions, but instead the success rate remains low. The log-linear test allowed to find significant relationships between some of the most important categorical variables in these actions: match status, number of intervening attackers and time. The decision tree models show that the number of players involved in these actions is the criterion that presents the greatest information gain. These results corroborate previous multivariate studies, although more research is still needed. Finally, the results of the present study can be used by coaches to create different training situations where success in this type of action can be enhanced.

Towards a contemporary player learning in development framework for sports practitioners

As it is appreciated that learning is a non-linear process – implying that coaching methodologies in sport should be accommodative – it is reasonable to suggest that player development pathways should also account for this non-linearity. A constraints-led approach (CLA), predicated on the theory of ecological dynamics, has been suggested as a viable framework for capturing the non-linearity of learning, development and performance in sport. The CLA articulates how skills emerge through the interaction of different constraints (task-environment-performer). However, despite its well-established theoretical roots, there are challenges to implementing it in practice. Accordingly, to help practitioners navigate such challenges, this paper proposes a user-friendly framework that demonstrates the benefits of a CLA. Specifically, to conceptualize the non-linear and individualized nature of learning, and how it can inform player development, we apply Adolph’s notion of learning IN development to explain the fundamental ideas of a CLA. We then exemplify a learning IN development framework, based on a CLA, brought to life in a high-level youth football organization. We contend that this framework can provide a novel approach for presenting the key ideas of a CLA and its powerful pedagogic concepts to practitioners at all levels, informing coach education programs, player development frameworks and learning environment designs in sport.

Maximal Strength, Sprint, and Jump Performance in High-Level Female Football Players Are Maintained With a Customized Training Program During the COVID-19 Lockdown.

IntroductionThe COVID-19 outbreak with partial lockdown has inevitably led to an alteration in training routines for football players worldwide. Thus, coaches had to face with the novel challenge of minimizing the potential decline in fitness during this period of training disruption.MethodsIn this observational pre- to posttest study involving Norwegian female football players (18.8 ± 1.9 years, height 1.68 ± 0.4 m, mass 61.3 ± 3.7 kg), we investigated the effects of a prescribed home-based and group-based intervention, implemented during the COVID-19 lockdown, on maximal muscular force production and high velocity variables. Specifically, maximal partial squat strength one repetition maximum (1RM), counter movement jump (CMJ) and 15 m sprint time were assessed 1 week prior to the lockdown and 12 weeks after the onset of lockdown. We also collected training content and volume from the prescribed training program and self-reported perceived training quality and motivation toward training.ResultsWe observed no change in 1RM [pretest: 104 ± 12 kg, posttest: 101 ± 11 kg (P = 0.28)], CMJ height [pretest: 28.1 ± 2.3 cm, posttest: 26.8 ± 1.9 (P = 0.09)], and 15 m sprint time [pretest: 2.60 ± 0.08 s, posttest: 2.61 ± 0.07 s (P = 0.52)].ConclusionOur findings suggest that a prescribed home-based and group-based intervention with increased training time devoted to strength, jump, and sprint ability, and regulated to obtain a sufficient infection control level is feasible and effective to preserve strength, jumping, and sprinting abilities of high-level female football players during a ∼ 3-month period of a pandemic-induced lockdown.

Risk Factors for Glenohumeral Arthropathy in Collegiate Football Athletes with Shoulder Instability

Dislocation arthropathy is a well-documented complication of shoulder instability. The risk factors for the development of this problem are not clear. We performed a radiographic review of the affected shoulder in athletes participating at the NFL combine with a history of anterior glenohumeral instability in an effort to determine whether delayed stabilization lead to higher grades of shoulder arthropathy. We secondarily were interested in assessing the risk factors that correlated with the development of glenohumeral arthrosis. Using available records from athletic trainers and personal interview, athletes participating in the NFL combine were assessed for a history of anterior glenohumeral instability. The number of instability events was recorded as a combination of dislocations and subluxations. Current age, age at time of injury, age at time of surgery, and player position were recorded. All athletes with a history of shoulder instability underwent radiographic testing including multiplane radiographs, MRI and CT scan. De-personalized radiographs of the affected extremity were reviewed by 2 independent physicians and graded using the Samilson and Prieto classification for dislocation arthropathy. Multi-variate analysis was performed to assess variables that predicted severity of glenohumeral arthritis including: age at initial injury, time from injury to surgical intervention, surgical vs nonsurgical treatment, and player position (offense vs defense). 334 athletes underwent a comprehensive orthopedic evaluation during a recent NFL Scouting Combine. 11.4% of players (38 athletes) reported a history of anterior glenohumeral instability with three of the 38 athletes reporting bilateral involvement over their playing career for a total of 41 shoulders. Players surveyed were on average 22.3 years old and 39.3 months from injury. Average age at the time of the initial instability event was 19.2 years. Within this cohort, the average number of instability episodes was 2.1 at the time of evaluation. Of the 41 shoulders, 78 percent of radiographs demonstrated at least Grade 1 glenohumeral arthrosis. Among the athletes that underwent surgical stabilization, those with longer delays between the onset of instability and the date of surgery had worse radiographic arthropathy (p=0.04). When comparing those athletes who underwent surgery to those who were treated non-surgically, those who had undergone surgical stabilization were more likely to have worse arthropathy than the non-surgically treated shoulders (p=0.02). Radiographs revealed a significantly higher grade of arthrosis amongst defensive players as compared to offensive players (1.37 vs 0.79, p=0.004). High-level collegiate football athletes with a history of anterior glenohumeral instability frequently develop radiographic evidence of glenohumeral arthrosis within a few years of injury. Longer time between initial injury and surgical stabilization was associated with more severe arthropathy on radiographic evaluation. Defensive players demonstrate a higher grade of arthrosis as compared to offensive players.

Factors of Japanese Football Players who Played in the Bundesliga for Multiple Years

The purpose of this study was to investigate the reasons why Japanese football players can play in the Bundesliga for multiple years. In this survey, we had interviews with five Japanese football players who played in the Bundesliga for over five seasons. The contents of the interviews were analyzed by SCAT (Steps for Coding and Theorization) method and extracted the same factors. As a result, it was found that they focused on building a relationship of trust with their coaches. They had the flexibility to change their playing style and position to match the coach's desired football style. In order to continue to be selected as a member of a match in the Bundesliga, not only high level football skills but also ability to adapt to the intentions of the coach are required. From the above results, it was suggested that in order to continue playing in overseas leagues, aspects other than soccer skills, such as tactics and understanding of the coach's ideas, are also important.

Theoretical Research on Football Tackle Technique

Tackle is one of the more difficult techniques in football technology to learn, and it has a wide range of applications in high-level football players. This article analyzes the principle, classification, and usage scenarios of tackles through literature method, interview method, and case analysis, and draws the following conclusions: 1. The tackle technique is a sequential and sporty open skill, which is unstable. Sex, complexity and difficulty. 2. The number of tackles and the success rate are the highest in the backcourt, followed by midfields and the lowest in the frontcourt. The reason is that tackles are mostly defensive tackles in the game, and the backcourt is the area where defensive tasks are the most important. 3. It is reasonable to classify the offensive and defensive attributes of tackles by area.

Динамическая позная устойчивость высококвалифицированных спортсменов, специализирующихся в игровых видах спорта

The production of manifold and rapidly varying movements in team sports requires maintaining an erect posture. This paper aimed to study dynamic postural stability in athletes engaged in team sports. Among the participants were high-level basketball players (n = 15), rugby players (n = 15) and football players (n = 12), as well as 30 young people not professionally involved in sports, all aged 18–21 years. Postural stability was evaluated using stability analyser Stabilan-01 (OKB Ritm, Taganrog). We utilized the Evolventa test, which simulates the real situation of tracking movements in the games, allowing us to quickly assess not only the quality of the athlete’s tracking movement, but also the reserves of maintaining the stability of erect posture. Classical and vector stabilographic characteristics of upright posture stability were analysed. To assess the quality of tracking, special game indicators were used. Athletes demonstrated a significant superiority in the accuracy of performing motor tasks and at the same time in maintaining postural stability over young men not playing sports (p ≤ 0.05). Noteworthy, basketball players had the highest tracking accuracy in the frontal and, especially, in the sagittal plane (p ≤ 0.05). Moreover, basketball players kept their balance much better, surpassing rugby players and, above all, football players in most indicators in both planes (p ≤ 0.05). Thus, the effectiveness, accuracy and speed of completing tasks, as well as fewer errors in high-level athletes were combined with an automated ability, due to the stereotype formed over many years of training, to confidently maintain an upright position even in the most difficult game situations. However, when analysing postural stability, one must take into account the specifics of the sports under study, where a wide variety of ball-handling techniques is combined with competitive activity of the hands or feet.

Genu varum and football participation: Does football participation affect lower extremity alignment in adolescents?

BackgroundGenu varum is one of the most common anatomical variations of knee alignment which is considered a risk factor for anterior knee pain and anterior cruciate ligament injury among football players. Considering that millions of children participate in high-level football training, the purpose of this study was to determine the genu varum development in adolescent football players and non-athlete peers. The hypothesis of this study was that genu varum incidence was higher in adolescent football players compared with non-athletic peers. MethodsThe design was a cross-sectional study. Two-hundred and thirty-seven male football players (FG) and aged-matched and anthropometrically similar non-athletes (CG) were recruited into the study. The quadriceps angle and intercondylar–intermalleolar distance were measured to evaluate the leg alignment. The distance between the medial edges of the condyles and malleoli was measured in millimeters using a digital caliper while angle measurements were performed using a photographic technique in a standing position. To analyze the variables, comparison, correlation and regression statistical tests were performed. ResultsThe intercondylar–intermalleolar distance and quadriceps angle values were significantly higher in FG than CG in all ages. In FG, a very strong correlation was found between number of training years and the intercondylar–intermalleolar distance. The prevalence of genu varum was markedly higher in FG than CG (~37% vs. 2%, respectively) based on intercondylar–intermalleolar distance. ConclusionThis study determined that the prevalence of genu varum and abnormal quadriceps angles in adolescent football players is significantly higher compared with their non-athletic peers.

Match High-Speed Running Distances Are Often Suppressed After Return From Hamstring Strain Injury in Professional Footballers.

Background:High-speed running is commonly implicated in the genesis of hamstring injury. The success of hamstring injury management is typically quantified by the duration of time loss or reinjury rate. These metrics do not consider any loss in performance after returning to play from hamstring injury. It is not known to what extent high-speed running is altered on return to play after such injury.Hypothesis:Match high-speed running distance will change after returning from hamstring injury.Study Design:Non-randomized cohort.Level of Evidence:Level 3.Methods:Match high-speed running distance in highest level professional football (soccer, Rugby League, Rugby Union, and Australian Rules) were examined for a minimum of 5 games prior and subsequent to hamstring strain injury for individual differences using a linear regression models approach. A total of 22 injuries in 15 players were available for analysis.Results:Preinjury cumulative high-speed running distances were strongly correlated for each individual (r2 = 0.92-1.0; P < 0.0001). Pre- and postinjury high-speed running data were available for a median of 15 matches (range, 6-15). Variance from the preinjury high-speed running distance was significantly less (P = 0.0005) than the post injury values suggesting a suppression of high-speed running distance after returning from injury. On return to play, 7 of the 15 players showed a sustained absolute reduction in preinjury high-speed running distance, 7 showed no change, and 1 player (only) showed an increase. Analysis of subsequent (second and third injury) return to play showed no differences to return from the index injury.Conclusion:Return to play was not associated with return to high-speed running performance for nearly half of the players examined, although the same number showed no difference. Persisting deficits in match high-speed running may exist for many players after hamstring strain injury.Clinical Relevance:Returning to play does not mean returning to (high-speed running) performance for nearly half of the high-level professional football players examined in this study. This suggests that successful return to play metrics should be expanded from simple time taken and recurrence to include performance.

Recommendations for initial examination, differential diagnosis, and management of concussion and other head injuries in high-level football.

Head injuries can result in substantially different outcomes, ranging from no detectable effect to transient functional impairments to life‐threatening structural lesions. In high‐level international football (soccer) tournaments, on average, one head injury occurs in every third match. Making the diagnosis and determining the severity of a head injury immediately on‐pitch or off‐field is a major challenge for team physicians, especially because clinical signs of a brain injury can develop over several minutes, hours, or even days after the injury. A standardized approach is useful to support team physicians in their decision whether the player should be allowed to continue to play or should be removed from play after head injury. A systematic, football‐specific procedure for examination and management during the first 72 hours after head injuries and a graduated Return‐to‐Football program for high‐level players have been developed by an international group of experts based on current national and international guidelines for the management of acute head injuries. The procedure includes seven stages from the initial on‐pitch examination to the graduated Return‐to‐Football program. Details of the assessments and the consequences of different outcomes are described for each stage. Criteria for emergency management (red flags), removal from play (orange flags), and referral to specialists for further diagnosis and treatment (persistent orange flags) are provided. The guidelines for return to sport after concussion‐type head injury are specified for football. Thus, the present paper presents a comprehensive procedure for team physicians after a head injury in high‐level football.

Effect of Weekly Training Frequency With the Nordic Hamstring Exercise on Muscle-Strain Risk Factors in Football Players: A Randomized Trial.

To examine the differences between performing Nordic hamstring exercises once or twice a week on hamstring eccentric strength and other muscle-strain risk factors in high-level football players. In this randomized trial, 32 football players (18-23 y old) completed an 8-week Nordic hamstring exercise training program in 1 of 2 experimental groups: group 1 (once a week; n = 15) and group 2 (twice a week; n = 17). Knee-flexor/extensor peak torques and biceps femoris long-head muscle architecture were assessed through isokinetic dynamometry and ultrasonography, respectively, before and after the training programs. Analysis of covariance, effect sizes (ESs), and t tests for percentage change were used to assess the effect of the 2 interventions on the outcome measures. Group 2 demonstrated higher hamstring concentric peak torque than group 1 posttraining (155-164 vs 149-158N·m; P = .043; ES = 0.27), although there was also a statistical trend for higher hamstring eccentric peak torque (212-234 vs 198-221N·m; P = .098; ES = 0.37), hamstring-to-quadriceps conventional ratio (0.56-0.59 vs 0.54-0.57; P = .089; ES = 0.31), and hamstring-to-quadriceps functional ratio (0.76-0.84 vs 0.71-0.79; P = .076; ES = 0.50). No between-groups differences were found for muscle thickness (P = .864; ES = 0.12), pennation angle (P = .289; ES = 0.18), fascicle length (P = .406; ES = 0.03), and quadriceps concentric peak torque (P = .340; ES = 0.02). Only the Nordic hamstring exercise training program performed twice a week strengthened the hamstrings of high-level football players, while similar changes in muscle architecture occurred with both once- and twice-weekly sessions.

Defining the attributes for specific playing positions in football match-play: A complex systems approach

ABSTRACT Introduction Talent identification and development programmes that retain and develop athletes are integral to the sporting success of National Governing Bodies in football. Currently, player attributes are studied in isolation without considering the complexity of interacting components of football performance. The current study applied a systems analysis framework to describe, in a structured and systematic way, the attributes for specific playing positions in football match-play. Methods: Eight high-level football coaches were interviewed. Models of the interacting attributes were developed for each position using Work Domain Analysis (WDA). Results: Six WDA models detail the attributes associated with each playing position. The models identified purposes of playing positions (restrict opposition actions, organise and coordinate, building up of offence, goal scoring and stretch opposition), performance-related measures and the functions required to achieve the playing position purposes (game play, psychological functions, time and space and player actions). Critically, the relationships between the purposes, measures, functions, processes, and objects are described in the models. Discussion The WDA models describe the interacting attributes of different playing positions in football match-play. The findings demonstrate football performance is complex, consisting of multiple interacting and dynamic components. Implications to support coaches in talent identification and development are discussed.

The association between visual exploration and passing performance in high-level U13 and U23 football players

ABSTRACT Purpose: The visual exploratory actions (i.e., scanning head movements) used by football players to perceive their surrounding environment have recently gained interest. While this has resulted in important findings relating to visual exploration during natural match-play, often the study designs lacked the experimental control of laboratory-based experimental settings. We aimed to investigate whether visual exploratory action is associated with passing performance for high-level U13 and U23 players in a controlled skill assessment setting. Methods: Fourteen U13 and 13 U23 football players from a Bundesliga club completed a standardised 32-trial sequence in the Footbonaut. Exploratory head movements were recorded with a head-worn inertial sensor, from which the count, frequency and excursion of head movements were extracted before and during ball possession. Ball reception and disposal were coded for each trial, and performance was operationalised as the time taken to complete each trial. Results: Across all players, visual exploratory action was associated with passing performance. The variables that best explained faster performance were 1) a higher number of head turns before receiving the ball, 2) a lower number of head turns when in possession of the ball, and 3) being an U23 player. However, different combinations of variables explained performance for U13 and U23 players. Conclusion: The findings demonstrate the value of scanning before receiving the ball to prospectively control passing actions in the Footbonaut. Future research should investigate the shared and contrasting characteristics of scanning actions, as they are observed by players in skill assessment tasks such as the Footbonaut, during training and during match-play.

The rise and fall of executive functions in high-level football players

IntroductionExecutive functions are higher-level cognitive functions. Despite being relevant to many aspects of everyday life, it is contentious whether executive functions are important for high performing athletes. Executive functions increase throughout the career of an athlete, yet it remains unknown what are the main contributors. Therefore, this study examined the effect of age and experience on executive functions in a cohort of high performing football players. MethodsData were collected over three seasons, resulting in a mixed longitudinal sample of 1018 observations in 343 male players (1–5 observations/player, age: 10.34–34.72 years; playing experience: 5–22 years) from the U12-Senior age groups of a professional German football club. Players participated in four cognitive tasks aimed at measuring higher-level cognitive functioning: a precued choice reaction-time task, a stop-signal reaction-time task, a sustained attention task, and a multiple-object tracking task, from which a total of eight dependent variables related to response time and/or accuracy were derived. ResultsLinear and non-linear mixed effects regressions were used to investigate the relationship between age, experience and executive functions. A second order polynomial revealed that, generally, a negatively accelerated curve best described the relationship between age, experience and executive functions. An increasingly smaller difference in executive functioning was generally observed between subsequent age groups, with a performance plateau evident around adulthood (~21 years old). Age and experience only explained a very low to moderate proportion of the variance in executive functions (marginal explained variance ranged between 2 and 57%). A significant age by field position interaction effect was only observed for the sustained attention task’s accuracy and response time components (p < 0.001). ConclusionsBoth age and experience showed a negatively accelerated relationship with executive functions in youth football players, and this relationship was generally field position-independent. These negatively accelerated curves seem to reflect those observed in general populations, where a plateau phase in the development of higher-level cognitive functioning is also observed around 21 years, reflecting the maturation of the central nervous system in normally developing individuals. Therefore, this study challenges the assumption surrounding the use and validity of executive functions as a measure of football performance potential in high performing athletes.

Readiness for career affordances in high-level football: Two case studies in Portugal

ABSTRACT This study investigates the factors driving football players with identical training experience and genetics to have dramatically different career paths. We studied two paired cases from a pool of 32 talented U-20 players who were twice World Champions. The first paired case is a set of monozygotic twins that played football for exactly the same period of time yet only one of them was selected for the national team. The second paired case refers to an outstanding player who got injured and withdrew from his football career and the player who replaced him in the national team. Semi-structured interviews were conducted and then analyzed inductively. The results provide a description of opportunities (affordances) that could only be taken by those who were ready to act skillfully when such rare event occurred. To act on such affordances (or not) may dramatically change the outcome of a player’s career. These results suggest that expert performance and high achievement emerge from circumstances resulting from the self-organization of several performer-environmental factors. Acting on such opportunities (affordances) implies being perceptually attuned to and ready for unpredictable events. This research builds on the ecological dynamics approach and provides a basis for further understanding of expertise and expert performance.

Defensive performance indicators in a high-level Spanish football team

Studies on football have gone from analysing technical and physiological aspects and assessing individual and collective behavioural elements to evaluating contextual variables that affect the development of the game. The objective of this study was to identify the strategic use of some technical variables to explain the defensive behaviour of the team or the players (as a group or individually) through the duels and recoveries that occur during the game. A team at the highest level of the first division of Spanish football (La Liga or Santander League) was studied throughout the 38 matches of the 2017/18 season. Principal component analysis was used to better identify the variables of the most important components that have the greatest influence on the two principal components. The results allow the defensive profile to be defined from a large number of official matches played by the same team. Variations in this game parameter depending on whether the match is played at home or away and the roles that are usually attributed to each player for each area of the field or each player’s technical characteristics are thus detected. Establishing performance profiles based on technical indicators using principal component analysis could be used to understand the individual and/or group performance of the team and thus manage the optimisation in competition of both the team itself and opponent teams.