Number one hits the balloon up, calls out the number of another player who must come and play the balloon high, calling out another number etc.
The player who hits the balloon must change places with the player whose name he called out.
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.