The castle (a gymnastics mat or bench) is defended by a goal keeper and his knights (the white team).
The blue attackers try to bomb the castle by throwing the ball at the bench / mat.
The goal keeper and the knights must constantly be moving to shield the castle and prevent a direct hit from the attackers.
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.