The aim of this study is to understand the head impact during actual collisions between American football players from Japanese universities. The subjects of this study were 23 players who belonged to T university in the Kantoh Collegiate American Football Association Division 2. We used a Vector Mouthguard (i1 Biometrics Inc.) equipped with 6 degrees of freedom (DOF) to measure the head linear acceleration (LA) and rotational acceleration (RA) as well as the head injury criterion (HIC), impact location, and number of impacts during collisions. The average number of collisions per player during a practice and during a game was 14.3 and 15.7, respectively. In terms of positions, the ratio (1:1.3) of total number of impacts for backs to linemen in Japan is lower than that (1:3) in the USA. Both during the games and practices, the range of 10 g < X ≤ 15 g in the average peak LA values was the most frequent, and the distributions were largely skewed toward low values (p < 0.05). The medians during the games and practices were 16.77 g and 15.87 g, respectively. The number of collisions during practices in Japan was significantly higher than that in the USA. Particularly, linemen undergo more head collisions than those of backs. Another common factor is that the impact of head collision during a game is significantly higher than that during a practice. However, data on Japanese university players is limited, and further data collection should be done before determining an accurate estimate of the practical concussion risk threshold.