Billy Slater's contrary conduct charge was downgraded by the NRL judiciary after the Melbourne fullback sensationally claimed he was provoked by a barrage of headbutts from St George Illawarra winger Jason Nightingale.

Slater's stunning defence means he will miss just this weekend's match against New Zealand Warriors instead of the two-game ban he had been facing for his role in the all-in brawl which marred Monday night's 26-0 win to the Storm.

The Test custodian claimed he only unleashed a flurry of punches on Nightingale after being headbutted three times by the Dragons flyer.

"The first two (headbutts) I let slip, until the last one, the last one was deliberate, I've seen him drop his head and head for my face," Slater said in the hearing which lasted just on an hour.

"It was not my mentality to throw punches until I was headbutted three times.

"I'm not pleading innocent, I realise ... it was the wrong thing to do."

Slater's defence surprised NRL counsel Peter Kite, who claimed he had no evidence of headbutts being launched, with video footage failing to shed much light on the incident.

Kite claimed the incident would not have escalated had Slater not intervened on the original altercation between Dragons half Jamie Soward and Storm half Cooper Cronk.

"There was no-one to pull away when you decided to run in," Kite said.

"There's no headbutt or anything of that kind."

After the hearing Slater said he would think twice before running in to help out a teammate involved in an altercation.

"There's no doubt I put my hand up and said I did the wrong thing by running in and obviously throwing punches, I obviously let down my fans out there and obviously let down my teammates this weekend as well," Slater said.

"Yeah, I'll definitely think twice."

Slater will now return against Gold Coast on Friday week, but will have 12-carry-over points hanging over his head in the run-in to the finals.

The downgrade will also boost his chances of taking out this year's Dally M medal with Slater to lose only three points for the one week ban, the Storm fullback believed to be in with a big shout of taking out the player of the year award following a string of spectacular performances.

Earlier, St George Illawarra forward Beau Scott took the early guilty plea as he accepted a one game ban for his role in the same brawl.

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