Brain Disease Is Pervasive in N.F.L., New Estimate Suggests

Using statistical techniques, a new study has arrived at a harrowing estimate: Three of four retired pro football players most likely had C.T.E. at death.Junior Seau, No. 55, during a San Diego Chargers game in 2002 against the San Francisco 49ers. His family donated his brain to research after his death in 2012, and he was later diagnosed with C.T.E.