When is a ball in touch?
The ball is deemed in touch when the ball or a player in contact with the ball, touches the touchline, the ground beyond it or any object outside the touchline. The ball is also in touch if a player jumps from on or over the touchline and makes contact with the ball before landing. Interestingly other players oo not count as objects for the purpose of touch

What is a zero tackle?
A zero tackle is called by the referee if the opposition previously knocked on or passed forward and advantage has been played. in the event of this occuring the next tackle will be called "zero", the following tackle will then be the first.

What is a differential penalty and why is it given?
A differential penalty is awarded for an offence at the scrum. Common offences include offside, loose forward not packing correctly or prop striking for the ball. A differential penalty differs from a full penalty in that a kick at goal can not be taken. A full penalty can only be given at the scrum for the use of offensive language or foul play. A full penalty is also awarded for offences committed before the scrum if formed.

How long can the tacklers hold down after the tackle has been completed?                              
According to the laws of the game "the tackled player shall be immediately released and shall not be touched until the ball is in play". A good referee will call move to assist the players in understanding when to clear the ruck.