STANFORD, Calif. (KTVU) -- Researchers with Boston University and the Department of Veterans Affairs found brain disease in former NFL players' brain tissue in a new study that was released this week.
The study examined brain tissue donated by 91 former NFL players after they'd passed away. Of the 91 samples, 87 samples had the brain disease Chronic Traumatic Encephalopathy or CTE, which can lead to memory loss and depression.
High school football players at Levi Stadium Friday night say they've experienced concussions on the field, where hard-hitting play has become part of the game.
"Four to five concussions," said Ryan Hogue, a junior at San Jose Pioneer High School. "I'd black out and be like where am I and be dizzy and all that, head hurting. Football's a contact sport. It's violent, It hurts and it happens."
Concussions are increasingly on many people's minds after the NFL was sued by 5,000 professional football players over brain injuries.
"There is no government regulated football helmet standard," said Fidel Hernandez, a graduate student at Stanford University who published a study on football helmet safety tests.
He and the team of researchers say their studies have discovered flaws in the safety tests used for NFL football helmets.
"The way the dummy head moves in that impact does not match the way a player's head moves with an impact with another player, the typical kind of football impact," Hernandez said.
Hernandez says the current helmet test only uses a dummy head on a metal pole and does not include a flexible neck that would mimic an actual player on the field where the head can rotate.
"That's significant because rotation is suspected to be one of the major causes of concussion," Hernandez said.
At Levi's Stadium, parents said they're glad to see high schools doing more to help prevent injuries and create protocols.
"There's a physical therapist on the field and they assess them and follow up," said Julie Fergus, a San Jose parent.
"I think that they are definitely trying to make it better for the kids. They can always do more," said Gina Inman whose son plays in San Jose.
The NFL said the number of concussions dropped 25% last season.
Stanford researchers say more research, better helmet testing and government regulation could make a big difference in players' safety.