Bending It Like Beckham: How to Visually Fool the Goalkeeper

Joost C Dessing,Cathy M Craig,Angela Sirigu

doi:10.1371/journal.pone.0013161

Abstract

BackgroundAs bending free-kicks becomes the norm in modern day soccer, implications for goalkeepers have largely been ignored. Although it has been reported that poor sensitivity to visual acceleration makes it harder for expert goalkeepers to perceptually judge where the curved free-kicks will cross the goal line, it is unknown how this affects the goalkeeper's actual movements.Methodology/Principal FindingsHere, an in-depth analysis of goalkeepers' hand movements in immersive, interactive virtual reality shows that they do not fully account for spin-induced lateral ball acceleration. Hand movements were found to be biased in the direction of initial ball heading, and for curved free-kicks this resulted in biases in a direction opposite to those necessary to save the free-kick. These movement errors result in less time to cover a now greater distance to stop the ball entering the goal. These and other details of the interceptive behaviour are explained using a simple mathematical model which shows how the goalkeeper controls his movements online with respect to the ball's current heading direction. Furthermore our results and model suggest how visual landmarks, such as the goalposts in this instance, may constrain the extent of the movement biases.ConclusionsWhile it has previously been shown that humans can internalize the effects of gravitational acceleration, these results show that it is much more difficult for goalkeepers to account for spin-induced visual acceleration, which varies from situation to situation. The limited sensitivity of the human visual system for detecting acceleration, suggests that curved free-kicks are an important goal-scoring opportunity in the game of soccer.

Highlights

In the game of soccer, the free-kicks scenario has become an increasingly important opportunity to score a goal
While it has previously been shown that humans can internalize the effects of gravitational acceleration, these results show that it is much more difficult for goalkeepers to account for spin-induced visual acceleration, which varies from situation to situation
Humans may have internalized the effects of gravitational acceleration, which remains constant across conditions [13,14,15], this is not viable for spin-induced acceleration that varies from situation to situation

Summary

Introduction

In the game of soccer, the free-kicks scenario has become an increasingly important opportunity to score a goal. If goalkeepers do not fully take the lateral ball acceleration into account when controlling their movements online, we predict that their movements should be biased in the direction of initial ball heading, away from the spin-induced lateral ball acceleration (Figure 1) [16,17]. If they do take it into account their movements should be directly aimed at ball arrival position. It has been reported that poor sensitivity to visual acceleration makes it harder for expert goalkeepers to perceptually judge where the curved free-kicks will cross the goal line, it is unknown how this affects the goalkeeper’s actual movements

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