Transcript for 'Concussion' and the Serious Impact of Repeated Head Trauma
Tonight you're about to meet the real life doctor who discovered that insidious disease found in the brains of athletes who suffered repeated blows to the head. And who paid a terrible price. Now after those countless concussions, even deaths, will smith's latest movie "Concussion," concerns are intensifying and people are questioning whether the beloved sport of football is simply too dangerous. Reporter: Vin is living the dream. Twice. ? I'm standing strong ? Reporter: Today at age 34, an aspiring artist in Nashville, married, father of four. His second shot at stardom. Manning. Ben utek. Reporter: For five seasons he performed on one of the biggest stages in America, the NFL, 150 million fans according to the league. Utek played in Cincinnati, won a super bowl with the Indianapolis colts. A bruising tight end, he dished out punishment and took it. At 28 it was over. A portion of his legacy not what he dreamed. At 28, to start experiencing memory problems. And cognitive changes. Was quite alarming. Reporter: A story that rings painfully true for more and more NFL retirees every season. Legends of the game. Chicago bear great Jim Mcmahon. Guys leave me a message and I'll erase the message thinking, I'll call them right back. Then I forget who just called me. Reporter: Hall of famer frank Gifford passed away from natural causes at the age of 84. His family had his brain studied and released this statement. "Our suspicions that he was suffering from the debilitating effects of head trauma were confirmed when a team of pathologists recently diagnosed his condition as that of chronic traumatic encephalopathy. It's become a who's who of former NFL stashes. Enough to line a wing of the hall of fame. Who have complained about or are diagnosed with ailments connected to repeated blows to the head. So much so even Hollywood took notice. The new film "Concussion" starring will smith as Dr. Ben anamalu, the real-life physician who diagnosed cte, a brain disease caused by brain trauma affecting a number of pro players. In a statement released today about the movie the NFL said in part, the NFL has made numerous changes to the game to enhance player health and safety at all levels of football. We are seeing measurable results including a 34% decrease in concussions in NFL games since the 2012 season." "Nightline" first reported on cte in the early days of Dr. Amalu's findings. I slept in the car probably a year and a half out of the last five years. Reporter: The Pittsburgh steelers Mike Webster won four super bowls. Famous, wealthy, revered. He died homeless, broke, and alone. Mike Webster died today. A heart attack took his life at the age of 50. Reporter: Believing that behavioral changes were caused by trauma to the brain, the nigeriaen born coroner performed Webster's extensive autopsy. The heart attack cannot explain his life after football. I had to provide an explanation for that. I was extremely disappointed when I opened up his skull and his brain looked Normal. Reporter: Determined to find answers, he analyzed Webster's brain and uncovered a new medical condition. We're looking at a region of the brain in a football player about 40 years old. And what you can see, it looks ugly. Reporter: He named it chronic traumatic encephalopathy, cte. The most significant contributing factor to cte is exporch Su exposure to blunt force trauma of the head. What happens is over sometimes 40 years you would not begin to manifest in a Progressive man similarly on course. Symptoms at mild as constant headaches. Very Sult changes in personality. Very subtle but diminishing intelligence. The mood disorders. Chronic alcoholism. Drug abuse. Are we talking general slaps to the head? Violent slaps that would make your brain move forward and backward, sideways, in your skull. Causing shearing injuries. Reporter: Amalu's published findings were dismissed, even demonized by fans and some in the NFL. What were some of the things people called you back then? Insinuated that I was a fool doctor, that I was fraudulent, that I was synthesizing my data and my findings. Some pretty much called me the "N" word. I actually lost my job. Even national institute of health officials had been told in the meeting, one of the officials said, that african, I don't trust him. Reporter: Someone who did trust him and bolstered Dr. Amalu's dribblety was neurosurgeon and former steelers team doctor Julian bales. We've got several linemen who did not have career-ending concussions who later were found at an early age to have extensive brain damage. Reporter: They collaborated for years. He's played in the movie by Alec Baldwin. The league has kept everyone in the dark. And you turn on the lights and gave their biggest bogeyman a name. What's happening now, what you think they're doing to you, that's nothing. Reporter: Though symptoms may be present for years cte can only be diagnosed after the player dies. Nobody informed them that there was a risk they could be damaged in their prime. Reporter: Hall of fame junior sand, one of the league's most beloved players, played on the field and his image off of it, retired from football and in time withdrew from his family. He commit suicide, shooting himself in the chest, which allowed doctors to study his brain. The mood swings and the depression, the insomnia was terrible. Honestly, I have a whole other level of compassion for what he went through at the end. He hid it so well. It doesn't help ease our pain and our grief, but understanding that he suffered from cte certainly is a big piece to the puzzle to help us understand part of the why. Reporter: In 2011, the class action lawsuit against the NFL over concussion-related injuries was filed. The case was settled in April 2015 without an admission of wrongdoing for over $1 billion to be paid out over the next 65 years to more than 20,000 NFL retirees. Bloomberg business estimates the NFL's revenue was $9.5 billion per year. These guys have been suffering for a long time. Both financially and mentally. And now it's going to be -- hopefully bring some relief to those families. Reporter: From peewee players to the pros, football is America's game. Beloved by millions. But as concerns deepen, parents have been pulling their kids off the football field. Last season, there were nearly 10,000 fewer high schoolers playing the game than the previous season. The issue honestly is not about concussion. No? It should be concern more about exposure to blows to the head. Reporter: As Dr. Amalu sees it those highly publicized concussions which the NFL hopes to address with its new concussion protocol are rare, compared to repeated blows to the head when the brain gets jostles to the skull in sports like boxing, hockey. Today more lawsuit were filed by more NHL players. Bottom line, is football too dangerous a sport? All I would say is that there are certain types of sports that are high-impact contact sports. Would you let your son play football? Having seen what I have seen in the brains of people who played football, I wouldn't let my son play. You think they're still in denial in ways? In some ways. Reporter: He insists he isn't out to take down America's favorite pastime, simply raise the safety standards. As a former college football player myself I went to the theater expecting to see a movie about football and concussions. But what I walked away with was a movie about an American hero from Nigeria. It's not a movie about football. It's a movie about our common humanity as for Ben Utecht, "Counting the days until my mind slips away" chronicles his battles with head injuries and the aftereffects. He like many NFL players forever grateful for what the great game gave them, now haunted by what it may have taken away. Movie "Concussion" hits theaters Christmas day.
This transcript has been automatically generated and may not be 100% accurate.