on the field. Just say subs have to be done by 10 sec left on the play clock. If they aren't done by 10 seconds left on the play clock, the offense can snap the ball leading to a "free play" for the offense for too many men on the field by the D. D has every right to sub. They just have to do it fast enough. No more of this 1 fat guy jogs to the middle of the field and taps another fat guy who jogs off.