There was no clear answer to my question, only compartmentalized memories.

In the house on the lake, which Kevin helped his parents buy, reminders of him appear at every turn. On the desk in his old bedroom is one of his Alabama playbooks; in the rec room are seven of his jerseys, framed; in the living room, there is his Philadelphia Eagles helmet and, of course, the giant flat-screen TV, which used to be his.

Kevin, who played for the New England Patriots as well as the Eagles, died after being treated for amyotrophic lateral sclerosis, also known as A.L.S. and Lou Gehrig’s disease. Kevin donated his brain to researchers in Boston who have examined the brains of more than 200 former football players after they died. The researchers said Kevin Turner’s brain was “riddled” with chronic traumatic encephalopathy, or C.T.E., which has been tied to repeated blows to the head.

When watching Sunday’s playoff games, you probably won’t think about Turner. But you should. In a life that was shortened by football, he made a wide and lasting impact on the sport.

After the diagnosis in 2010, Turner became one of the main plaintiffs in a class-action lawsuit former players brought against the N.F.L., claiming that the league hid the long-term cognitive dangers of the game. The league agreed to a settlement for potentially hundreds of millions of dollars, and the first payouts from that litigation are expected in the coming months.