Not illegal touching, as hitting Bubba in the butt is not a muff,bat or catch (7-5-13).
Not illegal forward pass, as it was going forward to the ground until Bubba's butt got in the way (7-5-2e exception).
Legal play.
Things to think about on spikes:
(1) If ball remained airborne ,it remains a forward pass and can be caught or intercepted.
(2) QB must spike the ball forward, if he turns and spikes it to his side, you may have a backward pass = open season on ball.
(3) Spike must follow a direct hand-to-hand snap. There has been some support to allow it from the shotgun as the big boys (NCAA) do. That support diminished last year when it was learned that the bigger boys (NFL) don't.