[stevesmith]

Okay, I think everyone is missing my point. This not about A, other than they committed a foul. This is about B gaining an advantage by fouling. Let's start at the beginning and look at all the possibilities.....

Same play, long run by A, we'll say 80 yard run.

1- Only A fouls near the end of the run. A is penalized from the spot of the foul. End result is a gain of 65 yards.

2- Only B fouls (live ball). In the example given, yardage is tacked onto the end of the A's run. End result is a gain of 85 yards.

3- A and B foul. End result is to replay the down.

My point is that because of A's foul, the best possible result for B is to also foul. By fouling, B loses no yards on the play, and A is actually penalized for B's foul. I don't think I can be any clearer than that.