A modification of moves like the Air Raid Crash, and a piledriver variation that seems more risky than those which are actually called illegal. It's a popular Japan/US move. There are several variations of the move.
Kneeling Belly-to-Back piledriver
The attack drops to their knees driving their opponent head first onto the mat.
Sitdown Belly-to-Back pilderiver
This variation is also called the Beach Break after its innovator Genki Horiguchi. The move has the attacker drop sitdown, driving their opponent's head into the mat.