Pass Interference?
 

A81 on the line of scrimmage and is covered by A82. A81 and A82 both go downfield. Pass is thrown toward A81. B36 commits pass interference.

A81 is guilty of ineligible downfield. B36 guilty of pass interference.

Do penalties offset?

If your stating B36 committed pass interference against A81 then pass interference will not apply. The reason's because defensive pass interference restrictions apply only to eligible receivers.

Not DPI.

Also, if ineligible A81 was the first to touch the pass you have Illegal Touching, 5 yards and loss of down.

NCAA: offset. No requirement that I know of for the Team A player being an eligible receiver. However, I'm going to have a very hard time flagging someone for DPI on a 50-79 player if they are the intended receiver (for whatever stupid reason). Do you NCAA guys have any problems with that?

Canadian Ruling
 

Canadian Ruling

Not DPI. PI can only occur against an eligible receiver.

If A81 touches the ball in an attempt to catch it then he is guilty of two fouls: illegally downfield and ineligible receiver touching. However, they both are 10 yard fouls applied at point of last scrimmage of which the defense has to choose one so the fact he is guilty of two does not matter.

Pass interference rules only apply to eligible receivers. No foul in NCAA for DPI.

If he caught it we have OPI. We had this recently on a swinging gate. WR covered the snapper...

No, in NFHS that is still ilegal touching. It no longer matters if it was caught or not.

I thought that was the case...
 

but wasn't 100% so I went with my WH on that one. I'll be sure to let him know...

7-5-10-a is your rule reference Ed.

Texas Aggie:

NCAA
7-3-8-c
Defensive pass interference is contact beyond the neutral zone by a Team B
player whose intent to impede an eligible opponent

It would not be offsetting. The DPI should be picked up.

What if A81 was not the first person to touch the pass and was not the victim of the DPI? What if A83 was the intended receiver and he was interefered with, but A81 was the ineligible receiver downfield? What have we got then?

Let's see if I can get this. We could have defensive holding and an ineligible downfield, penalties offset, replay the down.

Canadian Ruling
 

Canadian ruling:

We have DPI and illegal man downfield.

Case 1: If the DPI occurs 15 or more yards from the LOS then we have a 15 yard foul balanced by a 10 yard foul. The difference is 5 yards in favour of the offense. The automatic first down does not apply in a dual so we would repeat the down unless the distance is gained by the 5 yards.

Case 2: If the DPI occurs less than 15 yards downfield then it is treated as a 10 yard foul in a dual. These two 10 yard fouls net to 0 so we replay the down as Point of Last Scrimmage.

A81 is an ineligible down field. DPI against A83 does not change erase that foul. This is a double foul - replay the down. (10-2-1)