Head acceleration events are associated with tackler head contact and running speed during tackling in junior Australian football.

Tackling is the most common mechanism of head injury in junior Australian football (AF) and often a deterrent for participation. Instrumented mouthguards (iMG) have been previously used to assess head safety by measuring head acceleration, with no research in junior AF. Game iMG data was collected from 30 under (U)-13 boys and 30 U13/14 girls across 5 teams during one season. Footage of tackles involving players wearing iMG were reviewed using an established framework, divided into pre-contact, contact, post-contact, and event description phases. Tackles registering a suspected impact event on the iMG were labelled 'Hit' (n = 29), while tackles not registering a suspected impact were labelled 'No Hit' (n = 320). A random forest investigated if suspected impacts were influenced by tackle mechanics and player sex, which classified 78.1% of 'Hit' and 86.2% of 'No Hit' events. The most influential variables on random forest classification were: tackler head hit, tackle type, and speed of the tackler and ball-carrier (mean importance score >7). Our findings suggest tacklers may be more susceptible to substantial head acceleration than ball-carriers, given that tackler head contact (importance score = 7.98) was more influential than ball-carrier head contact (importance score = 4.67). Stationary or running tackles and bear-hug tackles most frequently resulted in 'Hit' events, indicating these should be a focus point for future tackle education. Finally, sex was not influential on suspected impact events. This study extends our understanding of how tackle mechanics influence head acceleration in junior AF, providing a foundation for further exploration.