I'm sure there have been guys who didn't realize they had a concussion and just kept playing. It's a violent game. The head injuries are the most dangerous to play with. We're trained to play no matter what. If you can run, and you're able to focus and know your responsibilities, you're usually out there playing. You wouldn't have enough players if no one played hurt. Especially if you're, like, on special teams, you're going to do everything you can to stay in the game.