Lacrosse participation in the United States has rapidly increased in recent years, however there is minimal research related to the sport. Existing research has mainly utilized laboratory-based testing procedures. There is a need to understand the physiological demands of players during live play to assist coaches with the training and conditioning necessary for improved player performance. PURPOSE: To compare player metrics of high school male lacrosse players during games and practices. METHODS: A team heart rate monitoring system with an internal global positioning system and gyroscope was used to record internal player metrics (heart rate [HR], calories) and external player metrics (duration, distance, speed, sprints). Participants in the study consisted of 13 male high school club lacrosse players (16.2 ± 1.5 yr; 175.3 ± 7.7 cm; 69.9 ± 13.6 kg). Subjects were monitored during two practices (130.9 ± 5.2 minutes) and one game (39.58 min). Differences in player metrics were compared by session, as well as by position: attack, midfield, defense, and face-off-get-off (FOGO). Game and practice data were compared utilizing paired samples t-tests, while individual position metrics were analyzed by independent sample t-tests. A standard p ≤ .05 was used to determine significance for the analyses. Effect sizes (r) were also calculated for each comparison. RESULTS: Significant differences and large effect sizes were found for average HR, total calories, and caloric expenditure (t ≥ 4.2, p ≤ .003, r ≥ .590). Significant differences and large effect sizes were also found for duration, total distance covered, and number of sprints between game and practice sessions (t ≥ 2.32, p ≤ .049, r ≥ .253). Positional comparisons identified significant differences and large effect sizes between midfield and FOGO positions for maximum HR (t = 2.411, p = .028, r = .525) and number of sprints (t = 3.242, p = .005, r = .745). CONCLUSION: The results of the study suggest that both internal and external metric requirements differ between high school lacrosse practice and game sessions, as well as across varying positions. This data could be used to alter practice sessions to better mimic the higher intensities of games and provide coaches the ability to train athletes at game-like and position-specific intensities.