Okay I need clarification:

If the pass is incomplete, we would enforce the roughing the passer penalty back to the previous spot (line of scrimmage) b/c it is a loose ball foul, right?

In this play of the day (8/21), the penalty is enforced at the end of the run (10 yard line) b/c the pass was completed, even though the penalty STILL occurred during the loose ball?

In this play of the day (8/21), the penalty is enforced at the end of the run (10 yard line) b/c the pass was completed, even though the penalty STILL occurred during the loose ball?

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Ref:

The best way to remember this enforcement is to "Give the offense everything they've earned on their own, and then tack on the penalty".

So in this case, marching off a 15 yard penalty would wipe out a 50 yard gain ....!

Give them their gain, add the penalty to the end of play.