In the Australian NRL comp, they have to complete a cognitive test at the start of the season. If they suffer a head injury, they have to go and resist the test on the side line. Get less than your preseason score, and you can't go back into the game. They are then tested again, and are not allowed back on duty until they meet that initial score.
Works pretty well, but it can open to manipulation, eg. Scoring deliberately poorly in your preseason test.
There is a similar protocol for RL in the UK, but I don't think it includes the sideline screening.