Third and goal on B's 10. Passer A-1 rolls out to his right and throws the ball at B's 9 which is intercepted by B-5 in his own end zone. B-5 swats away the hand of A-2 and exits the end zone to eventually get deflagged at B's 3. What are ways this can be enforced?
A-1 committed an illegal forward pass penalty at A's 9. B-5 then committed a flag guarding penalty in his own end zone.
If Team B declines the illegal forward pass penalty by Team A, then Team B has committed a safety due to the flag guarding penalty occurring in their own end zone. Two points are awarded to Team A, and it's Team A's ball at A's 30.
If Team B accepts the illegal forward pass penalty and Team A accepts the flag guarding penalty, then it's Team A's ball, replay down. This is a double foul (Rule 10-3-3C), so the penalties offset.