When you sign up to play football, you know there's a chance you might get hurt.

A new study, however, appears to confirm that for players who reach the highest levels of the sport, "chance" might be substantially higher than previously estimated, and the concept of "hurt" might be better understood as "sustaining potentially irreversible brain damage."

A team of Boston University researchers, including Ann McKee, a prominent neuropathologist, examined the brains of 202 former football players for signs of chronic traumatic encephalopathy, or CTE. The degenerative disease is caused by repetitive head trauma from concussive and sub-concussive blows and has been linked to the sport after being discovered in the brains of former players (CTE can only be diagnosed via autopsy).

The study's population included 111 brains of men with NFL experience and researchers found that 110 of them had the disease. It's a small sample size from a very specific population — but the near-ubiquitous presence of CTE makes the study's results troubling for football players and fans alike.

I should know. I'm one of the millions of former football players in the United States grappling with the effects that the game can have long after you've stopped playing.

'Shocking' results

For some, like linebacker Chris Borland, who polarized the football world when he retired after a stellar rookie year for the San Francisco 49ers, that means walking away before permanent damage. For others, like me, it means accepting the damage the sport can do and embracing its better qualities. I love to watch the sport and played at a high level in college and professionally overseas.

CTE has been a flashpoint for football over the past few years as the sport debates the treatment of on-field concussions at every level, from the NFL all the way down to local youth tackle leagues.

We’ve sort of become accustomed to it, but it is very shocking.

Former football players who were later diagnosed as having CTE exhibited erratic, sometimes violent behavior before they died, as the disease affects the brain's ability to function properly. The most notable case was Junior Seau, a Hall of Fame star who committed suicide in 2012 and was later found to have CTE (his brain was not included in the BU study).

The study found that 177 of the 202 brain samples (87 percent) had CTE, with the disease showing up in 48 of 53 samples (91 percent) of former college players and 3 of 14 (21 percent) samples of former high school players.

The brains of the ex-NFL and college players showed signs of more severe cases of CTE, while the disease's mark on the high school group's brains wasn't as pronounced. However, family interviews showed that members of all three groups exhibited the personality-warping symptoms of the disease before their deaths, which the researchers couldn't explain.

"There’s just no way that would be possible if this disease were truly rare," McKee said in a news release announcing the research. “I think the data are very surprising. We’ve sort of become accustomed to it, but it is very shocking.”

The results of the study did come with a major caveat: All the examined brains were from former football players. McKee told the New York Times that the samples largely came from former players who were afflicted with CTE's symptoms before their deaths, so their families chose to donate their brains for research, hoping for answers.

The study's limited scope is a concern for Munro Cullum, a University of Texas neuropsychologist who wasn't associated with the research but is considered an expert on concussions.

"It seems to be, perhaps, more common in people who play football," he told NPR, "but we don't know why. We actually don't know what the causative factors are or the risk factors [for CTE]. There still are probably yet to be discovered genetic and environmental factors that could be contributing as well."

McKee said that while the study does have its limits, the findings are still relevant. "I'm worried about these numbers steering the conversation in that these numbers are of a very biased brain donation research," she said to NPR. "But the fact that we found [CTE in 177 players] is cause for concern."

There are common little lapses that I assume other people chalk up to fatigue or overwork. I worry they're the first signs of my mind going as a result of football.

Some of the study's NFL brain samples came from famous figures, like Hall of Fame quarterback Ken Stabler, as noted in a New York Times feature profiling its disturbing results. The one former player whose brain didn't show signs of the disease wasn't identified at the request of his family.

Forty-four of the NFL brains came from linemen, which is the most common position and one that, as the researchers noted, sustains more of the subtle sub-concussive blows than other players, which could lead to higher rates of the disease.

Football going forward

The study is an important milestone in CTE research — Boston University touted it as "the largest and most methodologically rigorous CTE case series ever published" — but there's still more work to be done to understand exactly how football and the violence it begets affect the human brain.

The NFL, which was long resistant to the increasingly disturbing revelations about CTE and other concussion-related issues, finally acknowledged the disease's link to football last year, and has moved to adjust its rules for a less violent game. The league, which provided support for the study, issued a statement following the publication praising the research, claiming it will "continue to work with a wide range of experts to improve the health of current and former NFL athletes."

Helmet manufacturers are also working to develop "safer" designs, which aim to soften the concussive, damaging blows players will never truly be able to avoid.

More importantly, people who love football must come to terms with the research detailing exactly what the game could be doing to its players.

CTE could be quietly settling into my brain even now, years after my days on the field have passed. There are instances when I can't summon the right word, or grow overly emotional at odd moments, common little lapses that I assume other people chalk up to fatigue or overwork or whatever else. I worry they're the first signs of my mind going as a result of football.

One of the players profiled in the New York Times report was former Super Bowl champion Tyler Sash, who died at 27 of an accidental overdose of pain medications after exhibiting CTE symptoms. His family members said he played football for 16 years, so they had suspicions.

I played football for 16 years.

That doesn't mean that I have the same likelihood to have developed the disease as Sash, who reached the NFL, but the knowledge that there are documented cases of players who were found with the disease after spending a similar time with the sport is alarming.

“It is no longer debatable whether or not there is a problem in football — there is a problem,” McKee told the New York Times, giving the paper a hell of a kicker to close its coverage of the study. What she didn't say, however, is a much bigger question: What do we do about it?

The debate about football now is a personal one, that every player, parent, and fan will have to reconcile with themselves. We all have to decide if the real result of CTE is worth the risk, and if America's game can carry on even as it has the potential to destroy the brains of its players.