Concussion Substitutes

Football's growing understanding of the long-term risks of head injury in sport — echoing similar reckonings in rugby and American football — put increasing pressure on a rule that had barely changed in decades: a team suffering a suspected concussion had to use one of its normal substitute slots to take the player off, with no time and no incentive to make the safe call quickly.

IFAB approved trials of additional permanent concussion substitutes beginning in January 2021, with the Premier League adopting the trial from Matchweek 23 that February. The mechanism is deliberately simple: a team can make an extra substitution, beyond its normal allowance, specifically for a suspected concussion — removing the tactical cost that had quietly discouraged the safest decision.

The trial ran long enough, and was judged successful enough, that additional permanent concussion substitutions became a standing option in the Laws of the Game from 1 July 2024, available to any competition that chooses to adopt it. It is one of the newer entries in this history, and one of the clearest examples of the pattern running through all of them: remove the perverse incentive, and you don't need to rely on anyone reading intent correctly under pressure.