The truth of the matter is the
law 19.2 didn't anticipate such gamesmanship ; you have to take a view. For me red carding a sub seems harsh, It's not liked he punched somebody. how about 10.4
[laws]10.4
. Misconduct while the ball is out of play. A player, must not, while the ball is out of play, commit any misconduct, or obstruct or in any way interfere with an opponent.
Sanction: Penalty kick
The sanction is the same as for sections 10.4 (a)-(m) except that the penalty kick is awarded at the place where play would restart. If that place is on the touchline or within 15 metres of it, the mark for the penalty kick is on the 15-metre line, in line with that place.
If play would restart at a 5-metre scrum, the mark for the penalty kick is at that place of the scrum.
If play would restart with a drop-out, the non-offending team may choose to take the penalty kick anywhere on the 22-metre line.
If a penalty kick is awarded but the offending team is guilty of further misconduct before the kick is taken, the referee cautions or orders off the guilty player and advances the mark for the penalty kick 10 metres. This covers both the original offence and the misconduct.
If a penalty kick is awarded to a team but a player of that team is guilty of further misconduct before the kick is taken, the referee will caution or send-off the guilty player, declare the kick disallowed, and award a penalty kick to the opposing team.
If an offence is committed outside the playing area while the ball is still in play, and if that offence is not covered by any other part of this Law, the penalty kick is awarded on the 15-metre line, in line with where the offence happened.[/laws]