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 running back, as gaftfast as they can, they've moved the kickoff line forward so you have fewer of these instances where people are returning the ball at a high speed. lus you also find it is not just big blows that cause the problem but