The NRL's head of football Graham Annesley admits there could be more pressure on referees to sin-bin players but says new 18th-man rule changes will be difficult for coaches to exploit.
Incidents of foul play can now trigger an 18th man to be activated by NRL clubs after the Australian Rugby League Commission on Tuesday approved revised criteria around an extra substitution.
After consultation with clubs and players the ARLC signed off on changes to their controversial original proposal for an 18th man for three failed head injury assessments only.
That extra substitution can only be activated once three players suffer a concussion, or a player suffers a game-ending injury as a result of foul play in which the offender is sent off or sin-binned.
It is also under the proviso coaches have not used their allocated eight substitutions.
So far this season the 18th man would have applied just twice - for Cronulla in their round three loss to Parramatta when they lost three players to concussion and for Penrith in round two.
In that match, Canterbury winger Dallin Watene-Zelezniak was sin-binned for foul play on Nathan Cleary in the 70th minute and the Panthers halfback didn't return to the field.
Annesley said while the NRL encourages clubs to be responsible and conservative about taking players off the field who suffer head knocks, the 18th man rule will be hard to exploit.
"The three failed HIAs is a big factor in that," he said.
"It's not going to be easy for clubs to find themselves in that position, and we don't want clubs to find themselves in that position."
However, he concedes it could put pressure on referees to act by sending a player to the sin-bin in instances of foul play such as Felise Kaufusi's hit on Ryan Matterson in round two.
The Melbourne forward was penalised but not sin-binned for the shot that ruled Matterson out of the match and for the next two weeks of football, while Kaufusi was later hit with a two-week suspension.
"There'll be a bit more pressure on referees but they're already under that pressure," Annesley said.
"We saw a couple of weeks ago there was debate over whether a player should have been sin-binned and there's a bit more riding on that decision now potentially.
"Because you have to remember, it's not only the foul play but the player who is on the receiving end, they have to not return to the game."
Scrapped is the notion of the development player, which raised concerns about the effectiveness of having an 18th player on the bench for extreme circumstances in the first place.
The new rule approved for use from round five will allow clubs to select an 18th man one hour before kick-off from their 21-man squad named at the start of the week.
ARLC chairman Peter V'landys said the commission will be flexible with the changes and adapt them if need be.
"Player wellbeing is a priority for the commission and this additional safety net ensures players continue to be protected,'" he said.