NRL head of football Graham Annesley acknowledged people's opinion around the definition of foul play varied across the game but backed the referees and Bunker to find the right median.
The Titans lost winger Phil Sami to a head knock in Saturday's 42-16 win over the Knights after he copped high contact from back-rower Tyson Frizell early in the first half.
Sami failed a head injury assessment with Frizell only placed on report, while the former Dragon also escaped any charge from the match review committee.
Under the new 18th player rules, an 18th player can only be activated for foul play if a team loses a player for the match through injury when an opposing player is either sin-binned or sent off.
Titans coach Justin Holbrook voiced his thoughts on the incident post-match on Saturday, believing Frizell's hit was not worthy of a sin-binning but that a reportable offence should also be enough for an 18th player to come into play.
However, Annesley said with some reportable offences not picked up until the match review committee reviews the game, it would be hard to draw that line.
Graham Annesley weekly football briefing - Round 5
"The reason why players have to be sin-binned or sent from the field of play for the foul play provision of the 18th man to be activated is that it has to be a relatively serious incident," he said.
"In some ways because there was no charge in the Phil Sami incident it kind of backs that up.
"If the Titans got the opportunity to put an 18th player on in that incident and it's ultimately found Frizell did not commit an offence, that is an issue in itself.
"The referees and Bunker have to make a call on whether it was accidental, careless, reckless or intentional.
"They're the same decisions the match review committee make but the difference there is they (MRC) have got an unlimited amount of time to do that.
"They can have debates in the privacy and can talk about the seriousness of it.
"You haven't got the time to do that during the course of the game.
"There's not a perfect answer to this. The decision that the Commission made in implementing the rules around the 18th player were done so that we could try and find a happy median.
"It's a fine line, I don't hide from that fact that officials have to make their decisions quickly.
"People are making decisions based on their own judgement. There are accidents and will be times where heads will clash and players will get in awkward positions that they can't get out of."
Meanwhile, Annesley confirmed a no-try ruling against Knights centre Enari Tuala should've been given the green light with insufficient evidence to overturn the on-field decision.
Every try from Round 5
Tuala was awarded a try in the 47th minute by Ashley Klein before the Bunker deemed the ball had not touched the ground on review.
"I don't think there was enough evidence for the Bunker to have overturned the try," Annesley said.
"This is a tight call for the Bunker to make and with the referee right there [in the frame viewing the play]. In this situation, the Bunker should've gone with the on-field decision."
The Knights trailed 26-12 when the try was disallowed before conceding their sixth try of the afternoon four minutes later.
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