3.12 SUBSTITUTED PLAYERS REJOINING THE MATCH

(a) If a player is substituted, that player must not return and play in that match, even to replace an injured player.
Exception 1: a substituted player may replace a player with an open or bleeding wound.
Exception 2: a substituted player may replace a front row player when injured, temporarily suspended or sent off unless the referee has ordered uncontested scrums prior to the event which led to the front row player leaving the field of play and the team has used all the permitted replacements and substitutions.
(b) If uncontested scrums have been ordered and there is an injury to a front row player which requires that player to be replaced and there is a front row player available to replace that player then the front row player replacement must be used rather than players other than front row replacements.