Players still have the choice of “opting out” — rejecting the terms of the deal and suing the league as individuals — and at least a couple of Luckasevic’s clients will be among them. The N.F.L. will have to defend or make individual settlements with plaintiffs who opt out, including some notable ones, like the family of Junior Seau, one of the best linebackers in N.F.L. history, who at age 43 died by self-inflicted gunshot and whose autopsied brain showed the markers of C.T.E. (Of the 79 brains of deceased N.F.L. players that have been studied, 76 have shown what appears to be football-related damage.) There is the possibility that Seau’s family or other remaining plaintiffs could win a jury award well beyond the $5 million cap in the settlement, into the tens of millions or even more, but they will have to wait for a trial and then what is likely to be a drawn-out appeals process.

It is shortsighted, however, to assume that the N.F.L. and its owners will emerge from the settlement unscathed or that the league’s economic and cultural status are not under threat. Now that the N.F.L. has acknowledged that its product comes with dire health consequences, the sport, below the professional level, faces legal and regulatory challenges that will most likely intensify in the coming years. California recently passed a law barring state middle-school and high-school teams from conducting full-contact practices for more than three hours a week during the season; contact is not allowed at all in the off-season. California is always something of a trendsetter when it comes to lawmaking, as it has been with auto emissions, climate change and smoking bans. And as history has shown in the cases of smoking and other hazardous practices, regulation tends to expand over time: If a state can ban blocking and tackling in practice, what’s to prevent it from prohibiting those activities in games by banning football entirely or turning it into flag football? (Several other states, including Alabama and Texas, have similar restrictions on football practices.)

It is not easy in most locales to sue school districts, and in many cases, the dollar amounts on liability are limited. Nonetheless, schools are increasingly being sued over football. Parents of a high-school junior in Tampa who suffered a concussion on the sidelines after jumping for a pass have sued the Hillsborough County school district; he drove himself home, but later was put in a medically induced coma for nine days to reduce brain swelling. It’s possible that the very thing meant to protect players — new protocols that define how they should be evaluated for a possible brain injury, and how long they should be kept out of play if one is diagnosed or suspected — will actually put school districts, administrators and coaches at more legal risk. Now that they have, in a sense, been forewarned, what happens if they don’t follow the protocols or don’t have certified athletic trainers on staff or coaches smart enough to deal with possible concussions while they are also deciding on the right third-down play? What’s more, insurers may in time deem the sport too risky. Health insurers might treat it as a costly risk factor like smoking or a bad driving record. As football becomes more and more regulated, many districts may reasonably conclude that it’s more than they can handle.

C.T.E. and claims of football-induced brain damage are also likely to play a part in criminal trials, perhaps even some high-profile ones involving N.F.L. stars. “I can’t speculate on individual players,” David Franklin, a clinical neuropsychologist at the University of California, Riverside, School of Medicine, said when I asked him about this, “but you have to ask how the concussions issue changes the landscape from a law-enforcement perspective. I think it has to over time, because we now know that players are suffering repeated insults to the parts of the brain that cause changes in behavior.” Rates of smoking plunged and the industry declined because tobacco use could not be made safe. The N.F.L. may be at a similar juncture now. It has instituted rules changes to make its own games less violent and is funding and promulgating supposedly less dangerous ways to play at the youth level. But there is no assurance that any of it will make football any more healthful than low-tar cigarettes made smoking. The burden will fall on the N.F.L. to litigate the concussion issue in public and prove that its sport does not rob participants of their consciousness.

It appears the league may already be losing the argument with a segment of the nation’s parents. Between 2010 and 2012, Pop Warner, the nation’s largest youth-football program, experienced a 10 percent drop in participation after years of steady growth. It attributed the decline to concerns over concussions. There’s no reason to think its numbers won’t continue to fall.

Luckasevic’s files include medical and neurological assessments of his clients that would have been used if the case had moved toward a trial. He sent me one of them, with the name redacted. The player had a lengthy N.F.L. career and suffered blows to the head “too numerous to recall.” He had been knocked unconscious in games but never hospitalized. Now in his late 50s, he suffers chronic headaches, has stopped taking medications prescribed to alleviate them because they were ineffective, can’t concentrate long enough to hold down a job or maintain relationships and lives alone in the house he grew up in, where he passes his time watching TV. He has developed a tremor in his left arm and leg and is having difficulty swallowing.

The settlement class includes only retired players, not current ones. In an interview with The New Yorker earlier this year, President Obama, an avid Chicago Bears fan, said that if he had sons, he would not let them play football but he would remain a fan of the sport. “At this point, there’s a little bit of caveat emptor,” he said of the current N.F.L. players. “These guys, they know what they’re doing. They know what they’re buying into. It is no longer a secret.” When I talked to Luckasevic about the president’s remarks, he said: “But my guys didn’t know. That’s the whole point. They didn’t assume this risk.”