3rd and 20. Pass thrown to receiver R1, he jumps up to catch it, bats the ball down in attempting to catch it. He doesn't make the catch. Ball falls incomplete. R1 lands on the ground, and 1/2 second later is blasted by B2 from behind.
Flag for hit on defenseless player.
Is this a dead-ball (down-counts, 4th and 5), or can something like this, so quickly after the play is over, be considered a live-ball foul where we repeat the down (3rd and 5)?