Football is a rough game with a history full of attempts to limit the number of player injuries. Rules were enacted to reduce injuries, including early football's bans on slugging and hacking. Rules requiring seven players on the line of scrimmage and only one player in motion reduced the dangerous mass and momentum plays. Clipping, piling on, spearing, and targeting penalties are also intended to minimize injuries.
Till almost the end, there were a few holdouts. Bobby Layne was perhaps the most notable.