From 1996 to 2001, the N.F.L. gathered data in an effort to study the dangers of concussions. Whenever a concussion was diagnosed, the team physician was to record information like the player’s position, his symptoms and how much time he spent recovering.
As is common in such studies, players’ names and teams were represented only by codes, and the information is believed to have never been seen by more than a few committee members. There were 887 concussions recorded in all, forming a log that was consistently described as every head injury that teams had cared for during those six seasons.