For years, when it came to questions about the risk of permanent brain damage faced by players, the National Football League wasn’t just on the sidelines. It fought back against studies linking concussion to lasting damage known as chronic traumatic encephalopathy, or CTE, the degenerative disease that’s been found in nearly 100 former players.

The NFL’s commissioner, Roger Goodell, has been the dean of denial, saying about a decade ago, after the fourth case of CTE had been found in a former professional player, that there was no proof the man had suffered a concussion, suggesting instead that he might have developed the malady from swimming. And just before last month’s Super Bowl, with public awareness rising due to the film “Concussion,” Goodell announced that all sports pose risks. Perhaps eager to connect with his fans, he broadened the danger zone, saying, “There’s risks to sitting on the couch.”

But last week, the NFL began whistling a different tune. The reason for the abrupt about-face may be that the league took stock of the risks it faces, never mind players, and decided it needed to protect itself from future legal claims.

Regardless of the motive, the NFL’s confirmation that rough tackles and head injuries can lead to grave consequences is reverberating throughout the football world, all the way down to Pop Warner. The end of the NFL’s long denial means programs at all levels must face up to parental concerns, allowing families to decide what risks to accept in the sport.

The watershed moment came last week when Jeff Miller, the NFL’s senior vice president for health and safety policy, offered a startling response to a question from a member of the House Energy and Commerce Committee in a Washington, D.C., hearing room. Miller was asked whether a link exists between football and degenerative brain disorders. “The answer to that is certainly, yes,” Miller replied. The league’s spokesman confirmed that Miller hadn’t gone rogue — and the NFL accepts a connection.

That’s a big change from years of denials — which can be compared to the tobacco industry’s long refusal to accept that smoking causes heart disease and cancer. As recently as the early 2000s, the NFL’s committee on concussions was arguing, in reports in the journal Neurosurgery, that no player had developed chronic brain disease.

Then, in 2002, Dr. Bennet Omalu, a Pittsburgh neuropathologist who served as the Allegheny County medical examiner, studied the brain of the late Steelers center Mike Webster, who had died at 50 and had been suffering mental problems. Omalu identified CTE, which until then had not been found in football players, and published a report in the same journal. The NFL demanded a retraction, citing “serious flaws” in the research. The editors of Neurosurgery felt Omalu got it right. Gradually, more players were diagnosed, thanks to pioneering work by Omalu, whose story is told in “Concussion.” The NFL continued to refute the science.

By last year, the evidence on football and CTE had become overwhelming, just as the perils of smoking had been in 1997, when big tobacco threw in the towel. In 2013, the NFL reached a $765 million settlement with former players with brain injuries. The deal was approved in a federal court, but is on appeal because players have argued its terms should extend to any player, not only those in the settlement group. By stating the risks, and putting players on notice about them, the NFL may be trying to undercut future claims. With last week’s testimony, one legal expert told the New York Times, the NFL has now declared publicly that playing professional football comes with the risk of degenerative brain disease.

Now it’s up to those who love this sport, and love those who play it at all levels, to decide whether this risk is worth taking.