NFL Rules Question - Penalty Enforcement
 

https://youtu.be/5GEtlF6Zftg?t=3316

A few hypotheticals regarding penalties with a change of possession and no time remaining.

The only foul called was prior to the possession change. If Harrison had been tackled short of the end zone, would the Steelers have gotten an untimed down?

If the Steelers had been called for an illegal block on the runback, what would the result have been, given that the foul on each team would have been separated by a change of possession?

Obviously this play was quite some time ago, but it raises some questions that aren't obvious to a non-official. I'm primarily curious about the NFL, but I'd also be interested in how NCAA or NFHS would deal with it if anyone is so inclined.

If I follow your question correctly; under NFHS if there is a "double foul" during a play in which possession changes, and the team in final possession fouled prior to gaining possession, it is a "double foul" and the down is replayed.

If the team in final possession fouled after the COP, they can retain possession, and avoid a "double foul" situation by declining the opponents foul, but will be subject to the enforcement decision the opponent makes for the foul committed against them, or they can choose to enforce the "double foul" (and replay the down).

In this particular situation, with no time left at the end of the play, would the half then be over after the opponent enforced the penalty?

NFHS: In the first scenario with just one foul and he was tackled short of the EZ, since the foul occurred before the COP, there will not be an untimed down. If B (Steelers) accepts, the penalty is enforced from the previous spot giving the ball back to A (obviously won't happen). If B declines, the half is over. So, B will decline and go to halftime.

ajmc covered the double foul scenario. B would decline A's foul because accepting it would give A the ball back. A would then have to make a decision on whether to accept B's foul or not, which will depend on if B scored. If B scores, they will accept B's foul enforced from the spot of the foul and have an untimed down. If B does not score, they will decline and go to halftime.

So even though in the double foul scenario B is the team with the ball when they commit their foul, they would still get an untimed down if the penalty is accepted?

Yes. The logic is they have a right to keep the yardage they earned legally up until the point where they fouled. Combine this with 3-3-3a, and we have an untimed down for B.