Objective To determine the incidence, nature and causes of concussions sustained during men's elite professional Rugby-7s and Rugby-15s.

Design A prospective cohort study recording injuries classified as a time-loss concussion.

Population Players competing in the following tournaments: Rugby 15s—English Premiership (2007/2008 to 2010/2011), Rugby World Cup (2007, 2011), Pacific Nations Cup (2012, 2013), Junior World Championship (2008, 2010–2013), Junior World Rugby Trophy (2008, 2010–2013); Rugby 7s—Sevens World Series (2008/2009, 2010/2011 to 2012/2013).

Method The study was implemented according to the international consensus statement for epidemiological studies in rugby union; the main outcome measures included the number, incidence (number of concussions/1000 player-match-hours), mean and median severity (days absence) and cause of concussion.

Results The incidence of concussion in Rugby-7s was significantly higher than that in Rugby-15s (risk ratio=1.84; p<0.001). The severity of concussions were significantly higher in Rugby-7s than Rugby-15s (mean—Rugby-7s: 19.2, Rugby-15s: 10.1; median—Rugby 7s: 20, Rugby-15s: 7; p<0.001). The main causes of concussion were tackling (44.1%) in Rugby-7s and collisions (43.6%) in Rugby-15s. Significantly more (risk ratio=1.49; p=0.004) concussed players were removed immediately from the game in Rugby-7s (69.7%) compared to Rugby-15s (46.7%).

Conclusions Six actions were identified to improve the management of concussion in rugby: implement a pitch-side concussion assessment protocol; improve compliance with return-to-play protocols; work with referees to review the nature and consequences of collisions; improve players’ tackle technique; investigate the forces involved in tackles and collisions; and evaluate reasons for the higher incidence of concussions in Rugby-7s.