Leinster gave Castres a 14-0 head start when the sides met at Stade Pierre-Antoine last January. Matt O'Connor's men fought back to take a 29-22 victory that day and will be aiming for a similar outcome on Sunday afternoon.
There are referee associations in Connacht, Leinster and Munster and a referee society in Ulster:
Scrum Law Trials - The new Scrum Law trials.
Laws Of The Game - download the Laws of the game
Law Rulings - Clarifications on laws
Law Variations - age grade and sevens variations
Regulations - regulations
Equipment Approval - a guide to approved equipment