Players pass different kinds of balls for about 30 seconds.
After a sign of the coach (whistle or hand sign) players pass their ball on to another pair.
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.