Force is the result of energy exerted by a player which provides movement of the ball. The term force is used only in connection with the goal line and in only one direction, i.e., from the field of play into the end zone. Initial force results from a carry, fumble, kick, pass or snap. After a fumble, kick or backward pass has been grounded, a new force may result from a bat an illegal kick or a muff.
Tag: end zone
Rule 5, Section 3, Article 4
A ball touching the goal-line plane, when it becomes dead is in the end zone, even though it is moving away from the nearer end line and his its foremost point in the field of play.
Rule 10, Section 5, Article 2
The enforcement spot for any foul by the defense is the goal line when the run ends in the end zone and would result in a safety.
The Zebra Files 