[Mavdog]

this is clearly a foul and there is no way to characterize it differently.

when an offensive player leaves their feet they are judged to be fouled if a defensive player moves into the space where they should land.

here's the rule: A player may continue to move after gaining a guarding position in the path of an opponent provided he is not moving directly or obliquely toward his opponent when contact occurs. A player is never permitted to move into the path of an opponent after the opponent has jumped into the air.

the only question is if the defensive player had intent to move under the offensive player. if the ref believes the answer is yes, a flagrant (unnecessary agressiveness) should be called. that would fit the definition of a "dirty play" plain and simple.