Objective Interventions to reduce head injury range from law changes to technique training and education. The effective targeting of such interventions requires that the mechanism of injury be well understood. This study describes the events contributing to head injuries in Rugby Union.

Design An observational study with a cohort comprised of six professional Rugby Union competitions. Every Head Injury Assessment (HIA) reported during a three-year period was documented and described according to 15 descriptive criteria.

Outcome measures Descriptive criteria, and combinations thereof, including preceding and inciting event, tackle type, speed, direction and technique-related variables. The incidence of head injury was calculated per 1,000 events for each variable

Main results 611 HIAs were performed in 1,516 matches. 464 HIAs occurred after tackles (1.94 HIAs/1000 tackles). Active shoulder tackles, front-on tackles and high speed tackles have the greatest incidence of head injuries. For any tackle type and tackler position, the lowest incidence of HIAs occurs when the ball carrier is bent at the waist (1.2 HIAs/1000 tackles vs 2.4 and 9.8 HIAs/1000 tackles for upright and falling positions, respectively). For any ball carrier position, the greatest risk of head injury exists when the tackler is upright (2.7 HIAs/1000 tackles vs 1.9 and 1.2 HIAs/1000 tackles for bent at waist and diving, respectively).

Conclusions Technique components of the tackle, related primarily to the body position adopted by the tackler and ball carrier, significantly influence head injury risk. Interventions may be targeted at improving these variables to reduce head injury incidence in the sport.

Competing interests The primary author is employed in a scientific and research role by World Rugby (Pty) Ltd, who also funded the research study.