O'Brien was again left scratching his head when the bunker gave Cronulla's Mawene Hiroti a crucial late try in the Knights' 26-22 win over the Sharks.

It briefly gave Cronulla the lead, but only came after on-field referee Matt Cecchin had originally ruled he went into touch in trying to score.

An ill Kalyn Ponga later scored a 77th-minute matchwinner, easing the coach's stress levels.

But still, it came a week after he was left clearly frustrated by Enari Tuala being denied a try against Gold Coast.

On that occasion, the on-field call was a try before it was eventually overturned after several replays when the bunker ruled the Knights winger had been held up.

"I need to go back and have a look at the rules, my understanding of how it all works is a bit skewiff at the moment," O'Brien said.

"I'm looking at last week and Enari's try goes up. And we're looking at a billion angles that takes forever to talk ourselves into not giving the try.

"It gets taken off him. And an angle, shows the ball going down from end on.

"And then tonight we're watching a billion to talk ourselves into the try. So I'm confused."

O'Brien's issues with the NRL and bunker date back three games, where Tariq Sims scored a go-ahead try for St George Illawarra in their 22-13 win over the Knights.

The Knights said the NRL has since told him that Sims should have been penalised for an offside in the lead up, before he charged the ball down and ran away to score.

Under the league's new bunker system, the play was briefly reviewed as all tries are when awarded on the field.

"I haven't come in and criticised anything (previously)," O'Brien said.

"But I am confused and we've had some big calls: The Sims offside (in the Dragons loss), that's clearly a mistake.

"That was confirmed to us.

"I liaise with (referees' boss) Jared Maxwell and send them clips and correspond during the week

"We've had some big, big plays that have hurt this footy team and I just need to get a bit more clarification around it."

Australian Associated Press