With the N.F.L. regular season two weeks away, a new study revealed that one in four former players who died from 2016 to 2021 had C.T.E., a progressive brain disease. Researchers were conservative; the actual prevalence may be far higher, as only 235 of 878 brains were examined.

The league and players' union issued statements, but the N.F.L. emphasized reduced concussions, while the union called for action across football. OSHA officials, including former chief scientist Adam Finkel, called the numbers "apocalyptically high," yet noted the league remains too powerful to regulate.

Change may come from the bottom up, with parents and youth leagues delaying tackle football to reduce head impacts, potentially boosting flag football. The N.F.L. and union will discuss researcher recommendations.