After a crucial penalty late in Penrith's loss to Wests Tigers, coach Ivan Cleary admitted to feeling sorry for the NRL's referees as they fight an uphill battle to rid the game of the hip-drop tackle.

The illegal move has re-entered the NRL consciousness in recent weeks and involves a player swinging around and applying pressure to the lower legs of a rival with their hips or buttocks.

While players and coaches insist it is never made intentionally, the hip-drop tackle can cause serious leg injuries and has become prevalent in wet conditions, when defenders are likelier to slide around as they attempt a low tackle.

On Saturday night, Penrith's Soni Luke became the latest player scrutinised for laying a hip-drop tackle, with referee Adam Gee pulling the play back to sin-bin the hooker for his shot on Tigers forward Alex Twal.

The sin-binning forced the Panthers to play the majority of the final 10 minutes with only 12 men in a major blow to their chances of coming back from 12-8 down.

By the time Luke returned to the field for the final two minutes, the Tigers were closing in on a monumental upset.

While the risk of making a high tackle, shoulder charge or dangerous throw can be mitigated, Cleary questioned what Luke could have done differently in his tackle.

"I've seen a few like that now and the only way you can avoid it is to let go (of the ball-carrier)," he said.

"How do you tell a footballer to let go? That's my question.

"It was like (Brisbane five-eighth) Ezra Mam's last week, when he got suspended. The only way you could avoid that, as far as I could see, is if you let go.

"I hear the same questions each week and no one's got any answers."

Cleary also suggested on-field referees had begun to lump all hip-drop tackles together rather than police them on a spectrum.

In last week's clash between Brisbane and Parramatta, Eels forward J'maine Hopgood and Mam were both sent to the sin bin but only Mam faced suspension from the match review committee.

For his own hip-drop in that game, Broncos prop Payne Haas wasn't penalised on field but found himself banned for one week.

"We blend them all in together as the same," he said.

"I feel for the referees, actually, and whoever is making these calls because they've obviously been told and they're doing it."

While NRL head office has long insisted the onus is on players not to put their rivals at risk of injury, Panthers co-captain Isaah Yeo said that was easier said than done.

"You just have to have an awareness, I guess, but then it's a split-second thing," he said.

"You can feel like you're in a really good position and all of a sudden you're in a bad one just like that. It's a hard one."