O.J. Murdock, a 25-year-old wide receiver for the Tennessee Titans, died Monday from a self-inflicted gunshot wound, making him the sixth NFL player to commit suicide in two years. He was found in his car outside his former high school in Tampa, Fla., Monday morning. Murdock signed with the Titans a year ago, but never played a game for the team. His death reignites a debate over whether concussions, football-related head injuries and brain damage may be leading former NFL players to suicide.