To injure a defender easily, first at the main menu go to "Features", then to "Rosters". Go to the team that you will play. Go to every player and set their injury and toughness attributes to 0. Changing the other attributes is optional. Then, play against that team. Choose a running play (use Field Goal Fake Run after touchdowns). Once the running back gets the ball, run away from the line of scrimmage. Keep track of the yard lines to prevent a safety. Find an open defender on the way back. Sprint toward him (optional) and once you are very close to and directly in front of him, press Triangle. If done correctly, the defender will fall over and be injured. Note: The speed and timing will effect the length of the injury.