WEST COAST midfielder Murray Newman has been jailed for 12 months after being found guilty of fracturing a man's jaw at a Perth nightclub for sleeping with his girlfriend.

Newman was convicted by a jury last year in the Perth District Court of causing grievous bodily harm to Brett Marris, then aged 20, in November 2012.

Newman, then aged 18, had a "deep grudge" against Marris because he had slept with Newman's girlfriend, Judge John Staude said on Friday.

After weeks of threats from Newman on Facebook, including telling Marris to "start digging a grave", the pair saw each other at the Library Nightclub in Northbridge.

Newman was sober but "angry and agitated" when the pair fought briefly before bouncers broke up the fight, the court heard.

Judge Staude did not accept that Newman was acting in self-defence against a taller man.

"You struck Marris precisely because he would not rise to your challenge or a fight," Judge Staude said.

"You were the aggressor, not he."

Judge Staude was also critical of Newman for only showing remorse after the verdict and he concluded that a prison sentence was the only appropriate action.

Newman must spend six months behind bars before being eligible for parole and has a permanent restraining order against him and cannot be near Marris.

Newman was supported in court during the trial by West Coast teammates including captain Darren Glass, Dean Cox, Nic Naitanui and Josh Kennedy.

Murray has played four AFL games since being drafted at No.23 in the 2011 national draft. He was delisted by the Eagles at the end of last season but they stuck by him, placing him on the rookie list for this season.

West Coast released a statement saying the club "unreservedly accepts the court’s decision today to hand down a custodial sentence to Murray Newman."

Eagles chief executive Trevor Nisbett said in the statement that the club will continue to support Newman. 

"The club does not condone Murray’s actions, or similar violent acts, but will continue to support him," Nisbett said.

"As we have done throughout this case, we will continue to work closely with the AFL on this difficult issue.
 
"We would like to retain Murray on the club’s rookie list for the 2014 season as the club believes that it will be an important part of his rehabilitation and his re-integration to society – and football – upon his release.

"Since this incident occurred, Murray has been exemplary around the club, and is deeply sorry for his actions."