That could have led to further repercussions with the Green Machine getting docked the premiership points anyway after the fact.

In a positive, Stuart said at least young gun Xavier Savage would never forget his NRL debut - which lasted just 12 minutes in the Raiders' 22-20 loss to the St George Illawarra Dragons at Wollongong on Saturday.

Stuart brought Savage on at half-time after centre Sebastian Kris failed his head injury assessment.

It came after Dragons second-rower Jack Bird was put on report for high contact on Kris, who suffered blurred vision.

But the NRL's new rules surrounding the 18^th man meant he can only be activated if you lose a player through foul play and the offending player, in this case Bird, was sent to the sin bin or sent off.

That wasn't the case.

It took 12 minutes for the mistake to be realised before Savage was taken from the field.

Luckily, he'd flown his mum Erica down from Cairns just in case something happened. And did it what.

The NRL have asked for a please explain with further sanctions potentially to follow on Sunday.

Stuart was quick to take the blame for the incident, refusing to push any of it onto the NRL ground manager or the interchange stewards for allowing Savage on.

"In regards to that mess up at the start of the second half, that was my fault," he said.

"I thought it was when a player gets put on report I could use my 18^th man. I had an outside back on the bench.

"There's a lot of confusion that goes on, there's been a lot of rule changes this year and I get the mistake - I made it - so that's how that occured.

"Fortunately we didn't win. There would've been a big blue tomorrow if we had've won. It would've been disappointing to see what would've happened."

The NRL said the Raiders had clearly breached the rules for the 18^th man, which was introduced midway through this season.

Savage was hugged by teammates as he ran onto the ground, with Stuart shaking his hand.

He was then brought from the field after his 12-minute stint when the ground manager notified Raiders football manager Matt Ford.

"The rules are clear that an 18th man can only be activated if a player is sin-binned or sent off - or a team has three failed HIAs," an NRL spokesperson said.

"The Raiders incorrectly activated the 18th man at the beginning of the second half.

"The NRL has asked for full reports from the Raiders as well as our staff on duty at the ground to ascertain the circumstances which led to the 18th man being incorrectly activated."

While putting his hand up for the mistake, Stuart also felt the rule needed to be tweaked.

He said it should apply to all foul play - where a player was put on report or given their marching orders.

"If you want to look at a broader issue that's how the rule should be," Stuart said.

"When you lose a player to foul play you should be allowed to enact your 18^th man.

"But again, it was an error and I apologise."

Savage has been playing NSW Cup this season at either fullback or on the wing, having been recruited from Far North Queensland.

Stuart felt it would be the first of many NRL games.

"I just said to him after the game, 'At least you got a taste mate'," he said.

"He's a great young kid and there's a lot of first grade ahead of him. He'll certainly have a story to tell his kids one day in regards to how he got his first taste."