7. Jim McMahon
NFL fans remember McMahon for his thrilling Super Bowl season with the Chicago Bears. However, injuries decimated his career and caused him to abruptly fall into decline. In short, McMahon suffered an obscene number of concussions that affected his on-field ability and off-field life.
His form dropped dramatically and he never recovered. Eventually, the Bears had enough and traded him to San Diego. That kicked off a nomadic period for the quarterback and he only managed three more seasons as a franchise. To sum up, the game took its toll on the veteran.