[APG]

Originally Posted by mbyron

If the foul occurs beyond the end of the run, you would enforce from the end of the run.

From your comments, I gather that you're not a football official. Here's a crash course in enforcements.

1. High school rules deploy a concept called the basic spot, and a principle known as all but one.

2. Very simply: the basic spot is the end of the run for running plays and the previous spot for loose ball plays (a couple more precisely defined but not entirely transparent concepts).

3. Enforcement of penalties against the offense or defense is from the basic spot in all cases but one, namely a foul by the offense behind (closer to their goal) the basic spot. Those are enforced from the spot of the foul. All others -- all fouls by the defense, and fouls by the offense beyond the basic spot -- are enforced from the basic spot.

Hope that helps!

This was a great summary of penalty enforcements by mbyron. This concept is used at all levels of play. Just know at the NCAA and especially at the NFL level, there are exceptions to this rule which is why you may be confused.