A24 gets covered up on the end of the line by Wideout A95(A24 ineligible)
A24 goes down the field 15-20 yards
QB passes to A24
Safety B20 runs over to make a play and mistimes a play at the ball and knocks A24 to the ground clearly before the ball gets there.

What do we got?

NFHS
 

If A24 touched the ball (past NZ) then it's OPI. If not then just Ineligible downfield. Depending on the contact caused by B20 you could possibly call a block in the back or something of that nature, hard to say without seeing it.

According to 7-5-10(a), you can't have defensive pass interference against an ineligible receiver. So assuming the contact by B wasn't a personal foul, the only thing you would have is ineligible downfield if A24 didn't touch the pass or OPI if he did.

Canadian Ruling
 

DPI is against eligible pass receivers only.

Could have unnecesaary roughness though. That's 15+1D.

Re: Canadian Ruling
 

What is "unnecessary roughness?" If you are thinking it is a personal foul, it is not an automatic first down.

I thought the same thing at first, then looked at the author, its canadian ruling. :/

Heck, they can't even count to four. No wonder it's a weird ruling.

Weird? Or just different? Maybe the NFHS is weird with its "only five automatic first down" rulebook.

:) I think a rouge is more than different!