chris nowinski secured his brain for dr. mckee.iagnosed concussions, it seemed unlikely he had cte. >> i was fully prepared to see nothing. i remember late at night looking at the brain and thinking, "just going to knock this one off." and it just floored me. i just couldn't believe what i was seeing. >> narrator: such an advanced case of cte had never been found in such a young person. >> in, like, 20 spots in his frontal lobe. he's 21. he's so young. that changes the game to me. >> wrapped up and brought down by owen thomas. >> narrator: because he'd never had a diagnosed concussion dr. mckee suspected thomas might have gotten cte from the everyday sub-concussive hits that are an inherent part of the game. >> another nice play by owen thomas. >> those sub-concussive hits those hits that don't even rise to the level of what we call a concussion, or symptoms, just playing the game can be dangerous. >> the rock is home. a crucial matchup... >> mckee is saying, "look, this is very much an issue at the core of the game, of offensive l