George Visger remembers himself as a happy kid. A standout football player, Visger was tough on the field but affable and well-liked off it. His classmates even elected him to the principal’s advisory committee in ninth grade. “My mom raised six kids in a 1,000-square-foot, two-bedroom, one-bathroom house. And she said that of all her kids, I was the easiest going,” Visger tells me.

But that all changed after Visger had emergency brain surgery in 1981. At the time, the 23-year-old Visger was playing defensive line for the San Francisco 49ers when he started having daily headaches. A team doctor misdiagnosed him as having high blood pressure, only for Visger to learn he was suffering hydrocephalus, or “an excessive accumulation of water in the brain.” A night out drinking with teammates ended with Visger vomiting in his hotel room and experiencing focal-point paralysis in his right arm. Hours later, he was rushed to the hospital, where a neurosurgeon installed a shunt in his brain. All of it, he believes stems from the concussions he suffered while playing football, going way back to even his Pee Wee days.

Gone was the happy-go-lucky Visger, and in his place was an irritable man prone to aggressive outbursts. “All of a sudden, I became very short-tempered. My fuse…” Visger says, trailing off, searching for the right words. “I don’t handle stressors well like I used to. My threshold for irritation is almost nonexistent.”

The typical narrative for former football players suffering from brain trauma is one of internalized rage. Their depression, memory loss, impaired cognition and lower testosterone levels leaves them feeling helpless, weak and dependent. The story often ends with them dying alone — such as Mike Webster, the former Pittsburgh Steelers great who spent the last years of his life living out of his pickup truck, writing incoherent diary entries in an attempt to express his anguish — or in the most extreme cases, suicide, as with Dave Duerson, who won a Super Bowl with the Chicago Bears in 1985, but shot and killed himself in 2011 at just 50 years old. Both were found to suffer from chronic traumatic encephalopathy (CTE), a degenerative neurological condition caused by repetitive head trauma that’s been found in 79 percent of all former NFL players.

But a new concussion narrative has emerged in the past few years, and it’s arguably even more disturbing than the harrowing tales of suicidal retirees. It’s one of externalized rage — players becoming aggressive and violent in middle age, and liable to lash out at their loved ones, both verbally and physically.

Living with Visger, for instance, meant walking on eggshells. He never hit his wife or children, he says, but his anger and stature were intimidating enough. He’d explode on them for the smallest infraction, such as leaving the house messy.

Ultimately, Visger’s aggression cost him his family. His wife moved out six years ago when they lost their house, taking the children with her. After 20 years of marriage, they finalized their divorce last week. Visger now lives in a friend’s attic, and his only income is the $1,760 he receives each month in disability benefits from the Social Security Administration.

“We always had really nice times. And then slowly, things changed,” Debbie Tautolo says of her ex-husband Terry Tautolo, Visger’s teammate on the 49ers. “He would get angry, it seems, sometimes out of nowhere. … It got very violent. … The kids were always on guard. And finally they said, ‘Mom, he’s gotta go, or we’re gonna move out.’”

Tautolo’s behavior is similar to that of Tom Baugh, the former Kansas City Chiefs lineman who spends hours sitting alone in darkness, isolating himself from his family for fear of lashing out at them.

And their stories are far from the worst of it. In 2012, Kansas City Chiefs linebacker Jovan Belcher killed his girlfriend Kasandra Perkins before driving to the Chiefs practice facility and putting a bullet through his own temple. Five years prior, beloved professional wrestler Chris Benoit murdered his wife and son before hanging himself in his home gym. Like Webster and Duerson, both their brains showed signs of CTE.

I ask Visger, “Do concussions make football players violent and aggressive toward other people?”

“Yes. Absolutely,” he says.

Last January, Dr. Bennet Omalu — the neuropathologist portrayed by Will Smith in the film Concussion — was excoriated for saying he’d “bet [his] medical license” that O.J. Simpson suffers from CTE.

Omalu is no stranger to controversy. The NFL staged a smear campaign against him after he became the first doctor to diagnose CTE in a former NFL player (Webster) in 2002. But his statements about Simpson were especially inflammatory, and provoked the ire of people who thought Omalu was trying to somehow excuse Simpson’s behavior after leaving the NFL—specifically the 1994 double murder he’s widely believed to have participated in.

“Now, we’re getting in dangerous ground,” former NFL player Ryan Clark said on ESPN’s First Take. “It’s not irresponsible. It’s very irresponsible to say what [Omalu] is saying.” Clark resented the idea people might view him and other former NFL players as potentially violent just for having played in the league, and thought endorsing Omalu’s statements would make it easy for players to excuse their behavior. (He also implied Omalu was merely trying to drum up publicity for Concussion.)

A year and half later, Omalu stands by his statements. “When I said O.J. Simpson may have CTE, people attacked me for that,” Omalu recently tells me over the phone. “I was in no way justifying whatever his behavior was. But as a physician, I need to explore what role traumatic brain injury played in his behavior. This was a man who was pristine and had a gradual decline in his behavior — violent outbursts, couldn’t control his anger.”

It’s not just Simpson, Omalu continues. “A football player is more likely to be violent than someone who didn’t play, because of the brain damage. It doesn’t mean every football player will be violent, but there’s an increased risk,” he says. “This is a very inconvenient truth.”

Brain injuries (such as concussions) cause disinhibition, or the inability to regulate emotion and behavior, Omalu explains. “You start to become more emotionally driven, almost primal. You’re more likely to engage in violent and criminal behavior. You’re more likely to lash out. People with brain injury are more likely to have encounters with law enforcement, abuse alcohol and drugs. They’re more likely to have a breakdown of intimate relationships.”

Not all doctors are as certain of the link as Omalu, however. “There’s no research that shows a clean connection between head injury and violence, per se,” says L.A.-based sports neurologist Vernon Williams.

Williams agrees concussions can leave players disinhibited, predisposing them to violent behavior, and cause dysfunction of the amygdala, the area of the brain that regulates rage. But there are too many variables to conclusively say violent behavior is a function of playing the sport. The issue may get lots of attention, but the science is nascent, he says.

“We hear these anecdotes about NFL players committing acts of violence and assume it’s an issue of epidemic proportions. But that’s because of the sensationalism that occurs when it’s a famous person involved in a violent episode,” Williams tells me.

Williams is half-right. Contrary to public perception, NFL players are actually arrested half as often as the general population, according to a 2015 study from researchers at the University of Texas-Dallas. But the study also found that for violent crimes in particular, NFL players had a higher arrest rate for six out the 14 years studied. And a 2013 paper from researchers at Boston University, the country’s pre-eminent concussion research organization, found that violent behavior was common in former athletes (not just NFL players) with CTE. Of the 33 subjects found with the disease, half (51.5 percent) were physically violent while still alive, meaning they engaged in hitting, punching and other forms of physical abuse toward others.

Inconvenient, indeed.

Suggesting football factored into Simpson’s suspected killing of his ex-wife and Ron Goldman is deeply unsettling to people. A peer, in fact, told me I was being “irresponsible” for even broaching the subject.

The backlash is curious considering there’s already a well-established link between football-related concussions and another form of violence: suicide. There have been numerous high-profile athletes (many of them former NFL players) who have taken their lives in recent years, and were subsequently found to have CTE, including Junior Seau, Andre Waters, Ray Easterling, legendary BMX rider Dave Mirra and the aforementioned Duerson.

Football has remained shockingly popular in spite of these deaths and the overwhelming evidence that its players develop neurological disorders (such as Parkinson’s, dementia, ALS and hormonal deficiencies) at rates far higher than the general populace.

But saying football may cause players to commit acts of violence against other people strikes some as reckless because to accept it as truth would be to fundamentally change how we view the sport and the heinous acts its players commit. As long as the negative health effects of football are contained to those who play it, fans are able to effectively distance themselves from the sport and rationalize their enjoyment of it. But if playing football makes someone a threat not just to themselves, but to all of society, it becomes much harder for fans to justify supporting the sport.

“As long as we’re just killing ourselves, that’s okay [to people]. They don’t care,” Visger says. “But when we start killing innocent folks, then it’s an uproar,”

As Clark articulated on ESPN (in many ways, the NFL’s Pravda), the worry is people will view football players as inherently belligerent and inclined to violence. Or worse yet, that right-minded football players will use concussions to excuse their criminal behavior.

The issue gets even thornier with respect to players such as Simpson and Aaron Hernandez, the former New England Patriots tight end who was convicted of murder in 2015 and subsequently hanged himself in jail. Both players are universally reviled by fans, and to admit brain injuries contributed to their crimes would seemingly absolve them to some degree.

That said, talk of Hernandez and O.J. having CTE is entirely speculative at the moment. Hernandez’s brain is currently being examined, and Simpson likely won’t be diagnosed until after he dies. Even if they were found to have the disease, it’s impossible to say how much of their behavior was caused by CTE versus of their own volition. O.J.: Made in America, the exhaustive, eight-hour documentary about the running back’s life, portrays O.J. as a raging narcissist who (likely) killed his ex-wife after she refused to give him the control and validation he so desperately craved. Meanwhile, Hernandez had a reputation for violence dating back to his college football days, and it’s easy to see his murder conviction as an extension of that violent streak. But judging by CTE’s prevalence in former NFL players, Hernandez and Simpson would be in the minority if they don’t have it.

“Do I think there’s a link? Of course I do,” says Kimberly Archie, founder of the National Cheer Safety Foundation, a group pushing for more brain safety in youth sports.

Archie is a particularly vocal anti-football crusader — she filed a class action lawsuit against Pop Warner football last fall after her 24-year-old son died in an automobile accident and was found to have CTE — and she’s not afraid to speak to the controversy in the most inflammatory terms imaginable, no matter how uncomfortable. She believes O.J. and Hernandez both suffer(ed) from CTE, and the condition played a part in the murders they’re believed to have committed. “I understand it’s a crazy stance. But I want people to understand you can’t disentangle a person’s brain from their decision-making. And if your brain is damaged, there’s no way to say your damaged brain didn’t affect your decision-making. … I can’t separate Javon [Belcher’s] brain damage from his decision making. They’re interlinked.”

As evidence, she cites several studies linking traumatic brain injury to higher rates of aggression and violent criminal behavior. And she’s not alone in her assessment. “We have to rethink everything when it comes to the criminal behavior, bad behavior and weird behavior of former football players,” ESPN commentator Dan Le Batard said last January about Simpson. “We are headed toward a day where with a crime, the defense attorney is going to put football actually on trial. Where the defense is, ‘This behavior was caused because this sport made this guy hit his head too often.’”

It’s unlikely many NFL fans will share Archie and Le Batard’s thoughts on the subject anytime soon, however. After all, football participation rates remain surprisingly high in light of the research about the dangers of head trauma. The number of American boys playing 11-man, high school tackle football decreased by just 309 players nationwide in the 2015–2016 school year, according to a participation survey conducted by the National Federation of State High School Associations. And while several NFL and college players have famously quit the sport the past several years due to fears of brain trauma — including Michigan’s Jack Miller, UConn’s Casey Cochran and Chris Borland of the 49ers — the vast majority of their peers continue to play despite the inherent risks. Earlier this year, Cleveland Browns offensive lineman Joe Thomas admitted he’s already experiencing short-term memory loss, but still has no plans to quit playing football.

“As you see more and more of these murder-suicides from players, then things will happen,” Visger says. “But right now, it’s like ‘Hey, how ’bout those ’9ers?!’”