One in four dead football players had CTE. Why are we still flying blind?

A fall chill is in the air, football season is underway, and the Ice Bucket Challenge — a throwback to 2014 — is back in the news. Former NFL star Chris Johnson, who recently revealed that he is living with ALS at just 39, is helping revive the viral phenomenon that once filled social-media feeds with celebrities, athletes, and millions of ordinary fans dumping buckets of freezing water over their heads.

Johnson’s efforts come as football is confronting a range of unsettling neurodegenerative findings.