[PP]

Player a1 has possession of the ball under team b basket. Player a1 goes up but player b1 strips the ball out of a1 hands. He strips it so hard that the ball slams against the ground and hits the foam underneath the backboard. Play resumes.
The rule for the backboard mentions the top, the side and the framing but does not mention anything about the bottom of the backboard. Is there a rule for the ball hitting underneath the backboard?