I posted this during the game in response to a question about risk of subsequent concussions following a previous concussion. I was asked to re-post the information so that people could "hang their hat" on trying to sort out such a situation.
Originally Posted by CloakNNNdagger
Research suggests that if someone has already received one concussion, they are 1-2 times more likely to receive a second one. If they've had two concussions, then a third is 2-4 times more likely, and if they've had three concussions, then they are 3-9 times more likely to receive their fourth concussion.