His comments come after a Manly coach and three players were suspended for their involvement in the incident following a Harold Matthews Cup game between the Sea Eagles and Canberra Raiders that's believed to have left a Canberra school student concussed.

A spectator has also been issued with a ban, with everyone sanctioned given until the close of business on Tuesday to respond to their breach notices.

Manly assistant coach Jay Younis was the hardest hit, banned for 20 months on Wednesday, while a spectator has been banned from attending matches until the end of the year.

Three Manly under-17 players were also sanctioned: one until May 31, which ruled them out for the rest of the season, one for four matches and the other was given a two-game suspended sentence.

It's believed the incident started with two Manly players and a group of spectators exchanging words, which led to a spectator slapping one of the Sea Eagles juniors.

That's when a third Manly player became involved and the incident escalated substantially - hence why they were rubbed out for the rest of the season.

It's the second incident at a junior match involving Manly last month, with their SG Ball side also under investigation.

Trodden said they came down hard to send a message this sort of behaviour wouldn't be tolerated.

"It's completely at odds with the concept of sport, particularly under-age sport that you have an environment that is one that does anything other than promote safety and enjoyment," he said.

"Every time somebody crosses the line to threaten the ability to provide that environment we have to take stern action to make sure people understand that behaviour is not acceptable. I think that's what we've done.

"What people need to understand is if you engage in criminal behaviour ... then just because you're a spectator at a rugby league game doesn't mean you're exempt from sanction of the criminal law.

"Just like you wouldn't tolerate that behaviour on the street it should never be tolerated inside a sporting precinct of any type."

MORE RAIDERS NEWS

Trodden said they would also conduct a review of all grounds to ensure there was adequate space separating players on the reserves bench from the spectators.

Some grounds might need to leave some extra space behind the bench to help reduce the interaction with the crowd.

"One thing we'll be looking to make sure home clubs do is to have a clear separation between where reserve players sit and where spectators are so the opportunities for close interaction between spectators and players are reduced to a minimum," Trodden said.

"If a reserve bench is right up against the perimeter fence we'll be asking home teams to isolate an area around the back of the bench so the opportunities for close interaction are not as great."

The NSWRL are still investigating a separate incident involving the crowd at a junior representative game at Penrith on Saturday.