He has no business being on the field.

Players can be
Players not in the play shouldn't be but it's not criminal if they are
Same with coaches who may come out.

But there's no reason for an AD to jump onto the field during a play. None.

In fact, as pointed out above, he's worse than the average fan in that he has a specific duty to represent all that is rules based.

Tackle that sucker and arrest him like any other sucker with a field pass who thinks he can run onto the field during a play.