say they expect one-third of their repird players developing a cognitive problem. they say they guessed high because they tried to account for as many players as possible to take care of them from a medical standpoint. but one-third of players is pretty significant. average player a player dies from the nfl is 57. three times more likely to developed things like alzheimer's als and other cognitive problems. there's correlation that we've seen for a long time. he is the first player though to basically say, because of my concern, specifically brain injuries, cte, i'm making this decision. this may surprise you a little bit. he is a linebacker. you think those guys on the line are going to have the biggest blows to the head. oftentimes they do. but it is really more the speed players. quarterbacks, for example. running backs. players who are moving at a high rate of speed, then have collisions. or if you are a quarterback, somebody is coming at you at a high rate of speed. those injuries seem to be the most significant. it is not just the impact itself. but also what we call rotational impact. look at the way the brain moves in that animation there. it is not just a blow, but the brain is actually moving in a rotational force as well. that seems to be really more highly associated with concussions and subsequently cte. this animation shows the brain doesn't just take a blow, it changes its shape. it contorts. it moves in response to a blow, and that causes some of the damage even at the neuron level. >> a lot of players will stay from. they need the money, they love the game, whatever the reason, they've worked really hard to get there obviously. is there anything they can do to mitigate the risk? >> there's been a lot of talk of can you make football be a safer game and still be football. i think there's been some various things that have lapped at the league level to try and reduce the impact of these injuries. for example, the kickoff return is one of the fastest moving parts of the game. player gets the ball, they're