I don't know. Say you have a player skating backwards across the blue line with the puck. The player is in the zone but the puck is not. But before the puck crosses the player loses contact with the puck and the puck's momentum takes it over the blue line? Is that still onside? What if a goal was scored and a review was called for? Is it ruled a good goal? (We all know if the goal was scored on us, of course it would count.)