How much brain damage is too much? NFL players head for the exits.

The smartest player in the NFL just quit.

Not because he was unable to play, and certainly not because of his age–he's only 26. No, Baltimore Ravens' player John Urschel decided to quit because the risk of permanent, irreversible brain damage is just not worth it.

Urschel is a very smart guy. He's currently pursuing a Ph.D. in mathematics at MIT, one of the best and most demanding science universities in the world. Until this summer, he was (impressively) balancing his studies with being a full-time NFL player.

But when Dr. Ann McKee and colleagues published a new study showing that 110 out of 111 former NFL players had suffered serious brain damage, Urschel could no longer pretend he wasn't putting his future at grave risk. McKee's study, the largest study yet of chronic traumatic encephalopathy (CTE), showed alarmingly high rates of CTE in college and high school players as well (91% of former college players).

Let's get one point out of the way: everyone involved with the study, including Dr. McKee, knows that it was biased. The scientists examined brains of deceased players that had been donated to the study because family members–or the players themselves, before they died–suspected something was wrong. So perhaps the true risk of brain damage is lower than 99%. Maybe it's only 50%, or 20%. Do young men playing football want to take that risk?

John Urschel isn't the first player to quit because of the growing realization that football may cause irreversible brain damage. In 2015, San Francisco 49ers player Chris Borland retired at the age of 24, and in 2016 Kansas City Chiefs player Hussain Abdullah retired at 30, both over concerns about concussions and brain damage.

The NFL has been denying or downplaying the risk for years. A few years ago, after the suicide of former player Junior Seau, they announced a $30 million partnership with the NIH to study the risks of football on the brain. As results started coming in, showing that the risk was far more serious than most people knew, the NFL backed out of the deal with $16 million still unspent.

Meanwhile, the chorus of warnings has been growing steadily louder from the medical community. Last year, a former team doctor and a former football player and coach wrote in JAMA that

"unless there is a way to reduce the number of TBIs [traumatic brain injuries] caused by the sport, football will remain a threat to the brains and health futures of the players, including impaired cognitive function and reasoning, memory loss, emotional depression, and other sequelae that profoundly erode quality of life."

Earlier this year, a study out of the CDC reported that "3 high school or college football players die each year from traumatic brain and spinal cord injuries that occur on the field," most them as a result of being tackled during games.

Over the years, football players have grown ever larger (the average NFL lineman today weighs over 300 pounds) and the intensity of the violence on the field has grown with them. It's not just in the NFL, either: last year, three high school teams in the state of Washington forfeited their games against a local team out of a legitimate fear that players would be badly injured by the opposing team's 300-plus pound linemen. Their fears were justified: the human head simply wasn't built to withstand the repeated blows that players endure.

All players might do themselves a favor by listening to John Urschel. He explained his decision–and his abiding love for the game of football–in a lengthy interview on the Freakonomics podcast a couple of weeks ago. That interview should be required listening for young players, and even more so for parents who might be dreaming that their sons have a future career in football.

Will this be the end of college football? The risk of brain damage is startlingly high.

Parents send their kids off to college with high hopes and great expectations. Universities, in turn, have a responsibility to provide an education in an environment that supports and also challenges the students.

Universities are not supposed to encourage activities that may result in permanent brain damage.

And yet, they do. As revealed in a new report by Jesse Mez and colleagues from Boston University, just published in the Journal of the American Medical Association, a shockingly high number of former football players, from both college and professional teams, suffered chronic traumatic encephalopathy (CTE) later in life, likely as a result of their years playing football.

The study authors looked at 202 deceased former football players whose brains had been donated for research, and found that 87% of them had some degree of CTE. The highest rates of CTE were among former NFL players, which affected 110 out of 111 players. CTE was nearly as bad in college football players, though, with 91% of them (48 out of 53) suffering from CTE.

Over half of the high school players (27) had "severe pathology." The authors noted that in deceased players with severe CTE, the most common cause of death was neurodegenerative disease. As they also explain:

"There is substantial evidence that CTE is a progressive, neurodegenerative disease."

In other words, CTE is a death sentence.

The authors of the study stated their conclusions carefully, noting that the study was not randomized, and that players and their families may have been motivated to participate because they were concerned about a possible link between football and CTE. Nonetheless, even if the risk of CTE is much lower than found in this study, universities should be taking a very hard look at the risks that they are exposing their students to.

Or to put it another way, is it okay to ask young men to play football if the risk of permanent brain damage is only 50%? What if it's just 10 or 20%? Is that okay? Is football that important?

Readers of this column know my answer: no. College is not about football, and if it disappears completely, universities will be just fine. The University of Chicago eliminated its football program in 1939, and brought it back in decades later as much-reduced program, now in NCAA Division III. The university itself has remained a powerhouse, routinely ranked in the top universities in the country academically.

As I've written before, football is corrupting our universities, blinding them to their true mission (education and research) in the pursuit of a profitable entertainment business. University presidents seem helpless to stop or even slow down the enormous machine that is big-time college football. For example, in 2015 the University of Maryland (where I used to be a professor) paid millions of dollars to buy out the football coach, so that he could quit a year early and the university could pay millions more to a new coach. Ironically, Maryland had done exactly the same thing in 2011 to buy out the previous coach, at a time when the entire state had hiring and salary freezes in place. None of these actions benefitted the university or its students.

All the while, universities pretend that they are educating the players. Here's a quote from Bleacher Report's interview with star UCLA quarterback Josh Rosen:

"Look, football and school don't go together. They just don't.... No one in their right mind should have a football player's schedule, and go to school."

This from one of the top college football players in the country. (On this topic, Taylor Branch's 2011 exposé in The Atlantic is particularly worth reading. Or this article by a disillusioned former Michigan fan.)

Universities now face an ethical dilemma far more serious than merely taking advantage of athletes' skills to entertain football fans and pay inflated salaries to coaches. The JAMA study reveals that by running a football program, universities are not just robbing young men of four years that might be better spent getting an education and preparing for life: they might be robbing their students of life itself.