Hurdling is defined in Rule 2-15-1-a: "Hurdling is an attempt by a player to jump with one or both
feet or knees foremost over an opponent who is still on his feet." 2-15-1-b then says: "'On his feet' means that no part of the opponent’s body other than one or both feet is in contact with the ground."
When was the last time you saw somebody other than the ball carrier even attempt to hurdle somebody by those definitions, going feet first over somebody still on his feet?