COLLINGWOOD defender Marley Williams has been given a 12-month suspended sentence in a Perth court for a one-punch attack in 2012.

The 20-year-old had been on bail since a jury convicted him of grievous bodily harm in February.

There was an audible gasp in the court room from Williams' supporters when the sentence was handed down.

Williams had argued self-defence after admitting to punching Matthew Robertson, then 29, outside a nightclub in his home town of Albany in December 2012.

Robertson suffered a broken jaw in the attack, for which the maximum penalty is 10 years in jail, but Williams was given a 12-month sentence, suspended for 12 months.

Judge Julie Anne Wager said she accepted he had worked hard to address the issues that had led to the assault, which was at the lower end of the scale of GBH offences.

She also imposed a lifetime restraining order, preventing Williams from having any contact with Robertson.

She said she accepted the assault was not premeditated, that Williams was responding to an incident in the toilet, and that he was later distressed by his reaction.

"Had you been sober, had you been more mature, you would have let the matter drop," Judge Wager said.

"But for the aggression shown to you earlier, you would not have been involved in this matter."

The punch was "very forceful" but the victim had not been left with any long lasting effects of his injuries.

Collingwood football manager Rodney Eade provided a character witness statement, saying Williams was a very professional and focused footballer who was held in high regard by his peers.

Eade said Williams' behaviour outside the nightclub was out of character.

"I've seen Marley really grow.

"He's certainly regarded as a future leader of the club."

Williams issued a statement via the club on Tuesday afternoon expressing his relief at the verdict.

“I would like to apologise to all of those hurt, one way or another, by my actions," he said.

"I’m deeply sorry for the pain I’ve caused a lot of people. The last 16 months have not been easy for anyone involved.

“I want to thank my family, friends and football club for their support throughout an extremely trying time. I look forward to quietly getting on with my life with a new understanding of the harm one bad decision can cause.

“I have certainly learned that, regardless of the circumstances, you have to be strong enough to walk away. To be the better man.

“I’m relieved and grateful for the opportunity to return to football, a game I value and respect in a new way after what I have put myself and others through.”

Collingwood CEO Gary Pert said outside the court that Williams was "very relieved. At the same time he's very sorry for what he's created, not only to the victim and the impact that has had, but to his family and friends and especially to his mother. 

"This is something that's been out of character for him and he just wants the opportunity now to go on with life and be a better person. 

"As soon as he's physically and emotionally ready, signed off by the doctors and coaches, he'll be playing with our VFL team and then will be available to play in the AFL."

Williams has continued to train with his Collingwood teammates, but has not played while awaiting sentencing.

He has appeared in 22 games for Collingwood since making his debut in 2012.

Williams was supported in court by Pert, Eade and the club's welfare manager. 

Salvation Army Major Brendan Nottle also addressed the judge on Williams' behalf.    

The Pies ordered Williams to undertake volunteer work with the Salvation Army in the aftermath of the incident. 

"He's already put a lot of work in place, working with the Salvation Army, working on himself, and we don't expect - and even the courts said that - we would see any similar incidents like this," Pert said.

The judge issued Williams with a lifetime restraining order preventing him from contact directly or indirectly with his victim.

He’s not allowed to go within 50 metres of Robertson’s residence or workplace.

The prosecution has 21 days to decide if it wishes to appeal against the sentence.

It is not known whether Robertson intends to undertake any civil action.