Scientists have found that horned animals like muskox or bighorn sheep that head-butt each other do not escape unharmed and can end up with concussion and other serious head traumas.
The plan approved Friday could allow many former players to resubmit their claims of dementia caused by repeated head trauma from their time in the league.
A doctor said Tuesday the former NFL player had "severe" CTE when he allegedly shot and killed six people in April.
The former NFL player is accused of shooting six people before killing himself on April 7.
"You know you got no business researching it. Just go to your doctor," Howard Stern said on Tuesday.
"When I'm your age, what will matter to me is not my youth football career, but that like you, I'm a great parent," Favre says in a new PSA.
Researchers discovered an "abnormal" reduction of white matter in the brains of elite rugby players.
"It was a complete and total shock to me," Hernandez's lawyer said of his death.
Such damage has been seen only in people over 46. He was 27.
Hernandez ended his life in prison in April.
Boston University researchers will study the former New England Patriots player's brain for signs of chronic traumatic encephalopathy, or CTE.
Players had fought the deal because it doesn't cover future victims of brain disease CTE.
NFL officials denied the link as recently as February.
Heath professionals have written an open letter calling for a switch to touch rugby for young people.
The film, which opened on Christmas Day in the U.S., examines the brain-injury crisis.
The question isn't, "Is football dangerous?" It's, "Can it ever be safe?"