Two players stand on attack lines at either side of the net, while a third player stands between them at the net.
One of the players at the attack line passes the ball and then receives it back from the player in the middle, who now crosses the centre line, ducking under the net, before doing the same with the other player.
World Rugby has reportedly conceded Aaron Smith's disallowed try in the World Cup final should have stood.
"It is not only useful for staff who are experienced but a valuable tool for those subject staff who have to take teams."
The variety of sessions across sports - sometimes we steal session ideas from one sport and use them with another.