A recent study from Boston University delineates the pathophysiology of CTE as relating to abnormal deposition of the tau protein (whatever that is). Another study from the University of Michigan reports that former NFL football players develop early onset dementia or memory loss at a rate 19 times higher than the general male population between the ages of 30-49. There was even a sample from a teenage football player whose brain showed abnormal levels of the tau protein.
The bottom line is that football is an extremely dangerous activity. The dog fighter analogy is a stretch but these guys who play professional football for a living are indeed the gladiators of our age. Especially the interior linemen. And none of their contracts are guaranteed, that's the best part. These billionaire owners can cut a guy at any time, for any reason. Injury prone? Too many concussions? Out the door. So these guys play through it. They lace up their pads until they can't physically do it anymore. And too many of them are ending up like Hall of Famer and former Pittsburgh Steeler and Kansas City Chief Mike Webster after their playing days have ended. After retirement Webster suffered from amnesia, dementia, depression, and acute bone and muscle pain. He lived out of his pickup truck or train stations between Wisconsin and Pittsburgh, even though his friends and former teammates were willing to rent apartments for him. In his last years Webster lived with his youngest son, Garrett, who though only a teenager at the time, had to act as the parent to his own father. Webster's wife divorced him six months before his death in 2002. He was only 50 years old.
Webster is seen as an example of the difficulties American football players suffer when their careers are over. Other players who retired because of head injuries include Johnny Unitas, Merril Hoge, Troy Aikman, Steve Young, Joe Gilliam, Wayne Chrebet, and Al Toon, just to name a few.