Another sad story, former Chargers player Vincent Jackson- his autopsy confirmed CTE. He was only 38 when found dead alone in a hotel. He died from chronic alcoholism.
I think it’s a combo of number of incidents of verified concussions and how long you’ve been playing. I think just the amount of contact over a long career has to be a factor along with the knock-out type blows that these days force players to be examined under the tent with the new concussion protocols.