The NRL's long-term gender adviser has said some players may well be "education-proof", following a "horror stretch" of off-field incidents.

Key points: The NRL spends $8 million each year on player education and cultural change

The NRL spends $8 million each year on player education and cultural change A string of off-field incidents, including a number of players charged with assault, has marred the off-season

A string of off-field incidents, including a number of players charged with assault, has marred the off-season It's prompted the league to stand aside players charged with serious offences until the outcome of court proceedings

With several players facing assault charges resulting from the off-season, Professor Catharine Lumby — who has conducted evidence-based player education for the NRL over the past decade — said she did not know what more could be done.

"I can only conclude, I'm afraid, that a tiny minority of players are education-proof," she told the ABC.

"They know what to do but they don't care, apparently."

As the NRL launched its 2019 season in Sydney last night, it was still reeling from an off-season filled with player indiscretions.

Jarryd Hayne, Jack de Belin, Zane Musgrove, Liam Coleman and Dylan Walker are all facing assault charges.

The incidents prompted the NRL to announce a new policy last week that players charged with serious offences would be forced to stand aside on full pay, pending the outcome of legal proceedings.

That decision is being challenged again today in the Federal Court by de Belin, who claims the policy removes his presumption of innocence.

Just this week, Penrith Panther's player Tyrone May was charged with filming and circulating videos of sex acts with two women without their consent. The charges relate to alleged encounters in February and May last year.

'I have seen it this bad before'

Professor Lumby described player behaviour as "a crisis" for the game but said "we've seen it before".

"It has been a horror stretch in this off-season [but] I have seen it this bad before," she said.

"It's incredibly disappointing because if you take a longitudinal look, adverse incidents have gone down enormously over the past five years."

The NRL is spending $8 million a year on player education programs in an attempt to instil cultural change.

Professor Lumby has overseen three large research projects identifying current social attitudes and behaviours to better guide players.

Her research has shown that 95 per cent of players actually do the right thing.

Tyrone May is alleged to have filmed and circulated videos of sex acts with two women without their consent. ( AAP: Craig Golding )

However, she said, the latest off-field dramas had been "a big wake-up call to do better, try harder and to do a really strong review of where we're at".

"We've got a lot of things in place, but there's always room for improvement."

Professor Lumby said she had "zero tolerance for players who don't get it".

"Whether they like it or not they are role models," she said.

"They've got the privilege of playing in an elite sport, and if they don't like it they should get out."

Sports Minister Bridget McKenzie applauded the NRL for the steps it had taken to pull players into line, but said it would take time for the culture to change.

"If we're serious as a country about getting more women and girls into sport and participating in all those great games, then our elite male athletes need to be showing women respect," she said.

Rugby League great shown sex tape

Steve Mortimer came under fire for suggesting "young ladies" played a role in poor player behaviour. ( ABC News )

Rugby league great Steve Mortimer said he had seen first-hand the need for cultural change among players.

"Today I went and I saw a bloke that I absolutely respect in the game of rugby league, and I won't say who he is but he showed me this on his iPhone and I just could not believe it, that they were having sex," he said.

"I just thought, how embarrassing is that to yourself, and it should never be … shown that way."

Mortimer said players needed to do more to look after each other on nights out in public.

"When you go out, you've got to look after each other, and rather than trying to crack onto the girls … do what you have to do and then go home," he said.

"Obviously, they're human beings as well.

"I just think it's not just the players. I think it can also be the young ladies who are looking for a little bit of notice that, oh I've been taken out by a certain rugby league player, and that's just wrong," he said.

Mr Mortimer's comments came under fire on social media, with many on Twitter accusing him of "victim-blaming".

"I don't know what the answer is to fix it up, but I do know that all clubs can do with a lot more ambassadors to settle the players down," Mr Mortimer said.