MELBOURNE fullback Billy Slater last night successfully argued that his actions during an all-in brawl against St George Illawarra on Monday night were instigated by being headbutted three times by Dragons winger Jason Nightingale.

Slater had a grade-two contrary conduct charge downgraded at the NRL judiciary, and will miss just one game, after claiming that Nightingale had headbutted him during the fight that resulted in three players being sin-binned.

In explosive testimony, Slater told the hearing Nightingale had struck him with his head deliberately on one occasion and accidentally twice, provoking his reaction.

"The third one, that's the one I react to," Slater said. "As he flings me across, he hits me in the head, and then he goes in again. I reacted straight away to that. The first one, I let slip."

Slater said there was "no way in the world I would have thrown a punch" until the headbutt.

"I'm not saying what I did was the right thing to do," he said. "I'm not pleading innocent. I realise we're role models and I realise it's the wrong thing to do, but I wasn't of the mentality to throw a punch before I got headbutted three times."

Nightingale responded last night by saying: "Let him say what he wants. I wouldn't deny him the opportunity if it helps him get off."

NRL prosecutor Peter Kite said there was nothing deliberate about the clash of heads and claimed Nightingale had only defended himself.

During cross-examination, he said to Slater: "You're getting your head down, so is he, you make contact."

Slater replied: "I don't get my head down."

Kite: "There's nothing deliberate by Nightingale to headbutt you."

Slater: "I can understand an interpretation of accidental on that second one, but I think the last one was deliberate. You can actually see him drop his head and go straight for my face. I'm not saying [what I did was] right, but I was provoked."

The three-man panel of Mark Coyne, Don McKinnon and Bob Lindner were shown six angles of the all-in brawl. In a later incident, prop Jason Ryles was sent off for kicking front-row opponent Jeff Lima, although he was not charged by the match review committee.

Kite said Slater "ran a distance" to get involved in the melee.

"He was so committed he had to jump over player [Israel] Folau to get involved," he said. "From the moment he jumps, throwing his right arm over the pack, the matter escalates. It goes from what was a push and shove between a few players to an all-in brawl over the sideline. It's the action of running in that causes the escalation.

"Player Slater wasn't required to enter the fray to protect anyone, including himself. He ran in from a distance, six or seven metres, and he ran in in a very aggressive way."

However, Slater said initially he had attempted to pull Dragons centre Matt Cooper away from the brawl, but got caught up in the fight itself.

"I sort of reached over, grabbed his arm and tried to pull him away," Slater said. "I was trying to claw him, grab his arm or jersey, something that I could [use to] pull him back."

Kite argued that "there was no one to pull away when you decided to run in", to which Slater responded: "You don't think about those things when you're out there."

Slater's defence team, headed by Geoff Bellew, argued the actions of Dragons second-rower Beau Scott, who had pleaded guilty to a grade-one contrary conduct charge for his part in the brawl, were more serious than Slater's. "He doesn't just keep it [the brawl] going, he restarts it," he said.