Hand quickness and reaction drill.
Have a wide stance, holding the ball with 1 hand in front and the other hand behind.
You will let go of the ball and switch hand positions.
Keep doing this and gradually try to build up the speed.
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.