Trent Robinson has backed Spencer Leniu to continue playing with fire, even after his on-field spat with Keaon Koloamatangi cost the Sydney Roosters a penalty.

Leniu and Koloamatangi laughed off their on-field altercation after play on Friday night, after the pair's disagreement stopped play for more than a minute.

A fired-up Leniu initially earned a set restart when the pair became entangled in a tackle, but when he went on with it twice, the penalty went against the Roosters.

The 25-year-old then baited the South Sydney crowd when he came off moments later, holding a "bring it on pose" before eventually taking to the bench.

Leniu was not brought back on for the rest of the match, but was later spotted growing agitated when Latrell Mitchell put a big hit on young half Toby Rodwell.

Robinson admitted afterwards Leniu had gone over the line by giving away a penalty in possession, but backed the Samoan prop to maintain the rage in the finals.

"I want him to play with his natural spirit and just stay under the line," Robinson said following the undermanned Roosters' 50-20 loss.

"We spoke about it, and I'll encourage him to be himself and take on the opposition.

"And then he's got enough experience that he just should have regulated that and played the ball.

"But after that what did he do wrong? He creates an atmosphere when he's in that mode."

Two-time Sydney Roosters premiership winner Cooper Cronk labelled Leniu's behaviour as "stupid" in Fox's commentary, at a point where the Roosters trailed 10-4.

Koloamatangi also insisted afterwards there was no bad blood between the pair, who have been in NSW State of Origin camp together.

"I think it was good for the fans, a good spectacle leading into the finals," Koloamatangi said.

"We spoke about it after the game and had a laugh about it, so we'll leave it on the field and we're sweet.

"He's the enemy (when we're not playing together). He's not on my side, so whoever's not on my side is the enemy.

"I won't back down to anyone, but after the game we laughed about it and moved on."

The incident was one of two in the latest chapter of the usually heated rivalry between South Sydney and the Roosters, with both sides also clashing late.

Lachlan Hubner and De La Salle Va'a were both sin-binned following a melee, but neither side has any real judiciary matters to worry about.

"It's not a Roosters and Souths game without a bit of that feel and oomph," Souths veteran Cody Walker said.

"I thought Keaon handled himself quite well and gave us a penalty. You've got to expect those things when you're coming up against two arch-rivals.

"They go at each other on the field and leave it there."

Australian Associated Press