Background Head injuries are a concern in Rugby Union, accounting for 17% of injuries. Until the risk of specific game events is understood, effective interventions to reduce risk cannot be formulated.

Objective To describe the relative risk of head injuries in rugby.

Design Prospective cohort study.

Setting 1,516 Rugby Union matches in six professional tournaments.

Patients (or Participants) All players in the six professional tournaments were potential cases. Head injury events were identified by trained medical personnel using established Head Injury Assessment protocols.

Assessment of Risk Factors A professional video analyst evaluated every head injury event, and characterized it according to a pre-determined classification framework of 25 variables.

Main Outcome Measurements Head Injury Events characterized for relative risk by game event, playing position and match time.

Results 611 Head Injury Events (HIEs) were documented. Tackles had the highest risk of any game event, with a propensity of 1.94 HIEs/1000 events, accounting for 464 (76%) HIEs at a rate of 1 HIE every 3.1 matches. The tackler was 2.6 times more likely to be injured than the ball-carrier. Other high risk events included kick contests (1.57 HIEs/1000 events), mauls (0.7 HIEs/1000 events) and rucks. Rucks accounted for the next highest number of HIEs (73 HIEs at a rate of 1 HIE/20.8 matches. The player most likely to sustain a head injury was the flyhalf (68.9 matches per HIE), with the least likely the wings. Within tackles, backline players have a greater propensity than forwards (220 HIAs, 2.62 HIAs/1000 tackles for backs vs 240 HIAs, 1.54 HIAs/1000 tackles for forwards). HIE risk was unaffected by match-time.

Conclusions Tackles are the most injurious event, both by propensity and frequency. Tackling accounts for the greatest number of HIEs, and strategies to reduce the risk in tackles, with focus on the tackler, must be sought.