2/10, A-30 (time, score unimportant).
All Team A players have been stopped for more than one second, with 8 players on the line, and three players in the backfield, when end A88 gently begins moving, stepping with both feet to face his end line, and then continues his movement laterally toward the ball. After a few steps, A88 then veers into the Team A backfield, where he continues to move. Still moving (laterally), A88 is two yards behind the NZ at the snap. A11 receives the "shotgun" snap at the A-25 and immediately pitches the ball to A88 at the A-28. A88 catches the pass and advances to the 50, where he is tackled inbounds, and the ball is declared dead.
OK. We know that A88 was a lineman, and he may not be in motion at the snap. That would be illegal motion, 5-yards from the previous spot, repeat the down.
But, the question is: Is he an eligible receiver? To be eligible, by definition, a player of Team A must be the end player on the line, or a back. When A88 leaves the line, he is no longer a lineman. But, neither is he a back, if he doesn't stop for one full second. So, by those standards, he is not an eligible receiver. With that logic, when he touches the passed ball, he commits illegal touching.
As I said, this is kind of just an academic question, because the penalty for illegal touching by an originally ineligible player is also 5-yards from the previous spot and repeat the down. But, by extension, this could get more complicated if A88 goes downfield. He could be illegally downfield. If he gets blocked by B while the ball is in the air, there would NOT be pass interference.
Let me have it.