Background Concussion is one of the key player welfare issues in rugby union. A post-match assessment is a mandatory part of the head injury assessment (HIA) process in elite men’s rugby union, something unique to the sport and not seen in many other sporting settings. There is little evidence surrounding the potential value of this mandatory post-match assessment.

Objective To analyse at what stage of rugby union’s head injury assessment (HIA) protocol match-related concussions are diagnosed over the course of one season.

Design Prospective analysis.

Setting Twelve professional rugby union clubs in the highest league in England (UK) in 2019–2020.

Participants Professional male rugby union players who were diagnosed with a match-related concussion across all competitions.

Outcome measures Number and proportion of concussions diagnosed at different stages of HIA protocol: HIA1 (in-game, using an abridged version of the Sports Concussion Assessment Tool 5 (SCAT5); HIA2 (within 3-hours of match, supported by the SCAT5); HIA3 (within 48-hours of match, supported by the SCAT5); or outside of these windows.

Main Results There were 109 concussions (incidence 21.3/1000 player hours) across all competitions. 32 (29%) of concussions were formally diagnosed in game at the HIA1 stage. 65 (60%) of concussions were formally diagnosed at the HIA2 stage, and 9 (8%) post-match at the HIA3 stage. Three (3%) were diagnosed outside of the HIA window.

Conclusions The majority of formal diagnoses were made on match-day (in-game or post-match). However, the number of diagnoses made outside of this time period suggests that a later mandatory formal clinical assessment, based on the widely available SCAT5, can help clinicians to identify delayed presentations. As such, later assessments could help minimise the risk of players inappropriately returning to sport without following the appropriate graduated return-to-play protocol.