NRL referees boss Bernard Sutton has sent an email to all 16 clubs warning them that any attempt to slow down the play-the-ball will be penalised in round 19.

Bennett says the NRL's 10 metre crackdown this season had been a success but was not sure about their latest priority.

"If they really want to do something for the game they have to define when a tackle is completed," he said.

"That's the issue. It's when the tackle is completed.

"It is what goes on after that, it shouldn't be a grey area.

"They have won the battle with the 10m. I think they have done a good job there.

"Teams may be still leaving a little early but generally the 10m is a lot better than it has been.

"But the crucial moment in the game for me is when the tackle is completed."

Sutton emailed each club an attachment of footage from last round showing examples of ruck indiscretions that he vowed would not go unpunished this week.

The referees boss reportedly told clubs the referees would be looking for "flopping, leg pulls, spinning, crowding and climbing over a player" at the play-the-ball.

It's the latest crackdown, a month after NRL CEO Todd Greenberg called for an end to "nitpicking" from referees.

Told about the play-the-ball focus, Bennett said: "Gee I would love to see that.

"But we don't have a problem here with that.

"I got the email yesterday but I didn't even tell the players about it because it is not an issue for us here.

"We've got the quickest play-the-balls against us in the league, so we don't have to change."

However, Bennett doubted whether the NRL would be so vigilant on the new directive so close to the finals despite Sutton's email.

"They probably will not have a crackdown now as much as they are talking about it," he said.

"The season is seven weeks away from finishing.

"Hopefully next year they have a look at it a bit more, make a plan about going about that better."

Australian Associated Press