The scrum-half is the player who gets things going in the scrum.
It is their job to feed the ball into the scrum for the hooker to strike back to the number eight.
The scrum-half can roll the ball in from either the left-hand side or the right-hand side of the scrum.
The scrum-half must then not handle the ball until it has come out of the scrum.
The six other backs must be at least five metres behind the off-side line running through the hindmost foot of the last forward in the scrum.
If they are not, the referee will penalise the offending team.