Casey Cochran said he didn’t lecture Reed about the dangers of head injuries in football. He didn’t have to. The two have been friends since Cochran was 10. They used to throw passes to one another, to shoot basketballs together, saying things like, “If I make this last shot, I’m going to go to the N.F.L.” If Reed didn’t sink it, Cochran said, he’d shoot again and again until he did.

Cochran, a stereotypical coach’s son who slept with footballs in his crib, sustained his first concussion in eighth grade. With it came headaches and depression, so he sat out for a while. The stress of waiting to return to the game nearly smothered him.

After each subsequent concussion, he returned again and again, only to suffer yet another ringing blow to the head. But he continued to play because there was so much at stake: state championships, college scholarships, N.F.L. riches. Twice, he told me, he came within inches of killing himself — almost swerving into a tree while driving and, years later, holding a straight razor to his wrist — because he said he couldn’t bear the prospect of getting hit in the head again, and of dealing with the effects of a concussion again.

Cochran quit football for good in the fall of 2014, during his second season as the starting quarterback at Connecticut. In graduate school now, he said he still struggles with migraines, anxiety and depression.

In a phone interview last week, Cochran, who has become an advocate for concussion awareness, said quitting football was the hardest decision he has ever made, just as it must be the hardest decision any N.F.L. player might have to make.

“A lot of these guys feel trapped by the game because it’s scary to leave anything you’ve done all your life, but they have to know that they can survive outside of football,” he said. “Each person has to find it in his heart to make that decision.