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No one will ever know why Dave Duerson, the four-time Pro Bowl safety who played for the 1985 Super Bowl champs, the Chicago Bears, killed himself with a shot to the chest last week, at age 50, leaving behind four children, countless heartbroken fans and many puzzled, worried current and former pro-football players. "I saw him at a 25th anniversary party for our Super Bowl team in October, and he was terrific," says former Bears coach Mike Ditka, who led that '85 team to the title. "I don't understand."

Duerson, who earned an economics degree from Notre Dame in 1983, and a certificate from Harvard Business School's Executive Education program in 2001, had been a real NFL success story. Rather than just trading on his name, Duerson used his smarts and drive to build a thriving business career beyond his playing days. But lately he had fallen on hard times. His company, Duerson Foods, was forced into receivership in 2006. The year before, he resigned from the Notre Dame board of trustees after pushing his wife in a domestic dispute (he pleaded guilty to a misdemeanor charge of domestic battery). In 2007, Duerson's 17-room home went into foreclosure, and he filed for personal bankruptcy in September.

Yet most troubling of all, Duerson's ex-wife, Alicia, told the New York Times that Duerson was starting to suffer short-term memory loss. He complained of blurred vision and pain on the "left side of his brain." All of which raises the question, Did Duerson take that fatal step because he was despondent about his misfortune? Or did he end his life because he feared he would end up, like too many retired NFL players, depressed and confused, all because, medical evidence suggests, the game they loved cost them too many blows to the head?

The latter possibility was enough to send shudders throughout game, for good reason. "Please, see that my brain is given to the NFL's brain bank," he wrote on a piece of paper before his suicide. That bank, Boston University's Center for the Study of Traumatic Encephalopathy, has discovered that 13 NFL players, some of whom committed suicide, have suffered from chronic traumatic encephalopathy (CTE), a brain disease associated with dementia and depression. To date, all known cases of CTE involve victims who have taken repeated blows to the head, through contact sports like football and boxing.

As a member of a committee that evaluated the disability claims of retired players, Duerson was familiar with CTE. Within the next few months, the Boston University researchers will determine whether Duerson suffered from CTE, which can only be diagnosed postmortem.

Even if researchers find that Duerson had escaped CTE at this point in his life, his death could still be a turning point for football. Duerson's note, after all, proves that he could have died simply because he feared the disease. "It is very clear this has brought awareness of football's risk to a higher level," says Chris Nowinski, a former Harvard defensive tackle and co-director of Boston University's brain-research center. "It's very clear people can identify with what Dave Duerson appeared to be going through."

Because of his intelligence and generosity, Duerson surely could have rebounded from his recent troubles. Yet his last instructions were clear: Give my brain to research; I want to help figure out why football could cost lives, and find treatment. Because of this gift, because he could have died, in part, for a cause — improving the health of those who suit up — Duerson can really be viewed as football's first martyr.

"Stories like this, with Dave, really sink in," says Kyle Turley, the former offensive tackle for the New Orleans Saints, the St. Louis Rams and the Kansas City Chiefs, who suffered multiple concussions in his eight-year playing career. Turley, who says he has contemplated suicide, takes medication to control his moods. He says the drugs are working. "We all see it," he says. "Just being down there at this year's Super Bowl and looking those former players in the eyes, it was a very sobering experience. They all had that same look. It says, 'Only we know what is happening to us.' It's a scary thing."

So where does the sport go from here? "I hope this lights the fire under the concept of football reform," says Nowinski. "The fact that we have pitch counts in baseball to protect kids' elbows but no guidelines for coaches about how often kids can be hit in the head, this late in the debate, is crazy." While most of the football players diagnosed with CTE played in the NFL, the Boston University researchers found early evidence of the disease in an 18-year-old who only played through high school. At least two college players, including University of Pennsylvania defensive end Owen Thomas, who committed suicide in April, at age 21, showed signs of CTE.

Fewer exposures to head collisions can only reduce the chances of long-term damage. What if kids didn't play tackle football, with helmets and other equipment, until high school? What if all youth leagues became flag football leagues? A kid can learn proper tackling technique as freshman in high school — where coaches, in general, are more qualified than those in Pop Warner groups — and still become the next Ray Lewis. "Would you let your 12-year-old go to boxing class and let him get punched 1,000 times in the head each fall?" asks Nowinski. "You wouldn't. But we let that happen with our football players."

The boxing analogy is fitting. Some have wondered whether football will eventually mirror that sport, and become a fading niche affair that is too violent for mainstream tastes. That still seems like a stretch. Corrupt and dysfunctional organization, more than anything else, cost boxing, though deaths in the ring certainly turned off fans too. The NFL's economic engine, the pageantry and big business surrounding the college game and high school culture of Friday Night Lights will always keep Americans plugged into pigskin. The incentives are especially strong for kids from poorer areas.

But Duerson's suicide – especially if researchers diagnose CTE — should still be a game changer. Even in high school hotbeds like Texas, don't be surprised to see the best athletes forsake football for other sports. The fans will go to the games, but enthusiasm may wane. Upper-crust high schools, with no history of producing college athletes, should cut programs. So should lower-tier colleges. Why should education funding harm, instead of enhance, the brains of students?

Football can't stay on its current course. It must become a safer game, or live with less people playing, and enjoying, the sport. "What Dave Duerson's death means is that we've got a lot of people out there suffering silently," says Nowinski. "The reality is, if they have this disease, we're not sure what they're going to do next."

Gregory is a staff writer at TIME. Keeping Score, his sports column for TIME.com, appears every Friday. Follow him on Twitter at @seanmgregory

• Sean Gregory
• We will never know if Dave Duerson took his own life to save other football players. But his last message proves they were at least on his mind