They are also focused on doing whatever they can to spare another family their suffering.

On a night out with friends on April 16 last year, Mr Cronin entered the maelstrom of a bar brawl at The Windy Mile hotel in Diamond Creek to drag out friend Anthony Hopkins.

It was during this act that the 19-year-old was punched, without warning, to the right temple by Andrew William Lee, who had been watching from the side. Mr Cronin got Mr Hopkins out of the brawl and left the hotel with friends, but his condition worsened over the next two hours and he died in hospital the next night from bleeding on the brain.

On Friday, Lee was jailed for eight years for manslaughter. He will serve at least five years before parole.

CCTV footage released by the court shows Lee stepping into the brawl to strike Mr Cronin. The footage was shown to the jury in black and white, but following Lee's guilty plea, it was enhanced to highlight Lee coloured red and Mr Cronin coloured green.

Justice Lex Lasry told the 34-year-old father - who is proficient in Muay Thai and continued brawling with others after throwing the fatal punch - he should have followed the example set by the younger man.

"You should have remained standing and watching, or preferably followed the example of Patrick Cronin and done what you could have to have prevented the fight from continuing," Justice Lasry said.

"It is significant that the one person who suffered the terrible consequences of this incident was the person whose behaviour featured no aggression whatsoever.

"On any view, you acted violently and that violent act had a dreadful consequences."

Outside the Supreme Court, Matt and Robyn Cronin said their son had died after doing what he had been taught: to look after his friends. Lee also had a choice that night, Mr Cronin said, but opted for a coward's punch.

Patrick's brother, Lucas, added: "The judge said it well, that everybody should be acting like Pat acted ... that's a great way to remember Pat."

After 19 months of court appearances, the Cronins were relieved Lee had been sentenced. That relief was shared by their dozens of supporters, some of whom clapped when Justice Lasry left the bench. The large group planned to get together on Friday night to remember the cheeky, friendly, caring teenager who was a promising footballer for Lower Plenty and an aspiring physiotherapist.

The Cronins believe the wait for justice was unacceptably long, and that Victoria's one-punch laws - which carry a mandatory 10-year jail term - will never be used unless lawmakers amend the 2014 legislation.

Lee was originally charged with murder but prosecutors downgraded the charge to manslaughter. He went to trial on that charge but pleaded guilty days into his trial when prosecutors withdrew a request for Justice Lasry to impose the mandatory term.

Prosecutors conceded they could not prove Lee intended to punch Mr Cronin.

The Cronins said on Friday the one-punch legislation was poor and ambiguous.

"Our most basic understanding, and I am not a lawyer, is that manslaughter is murder without intent," Robyn Cronin said.

"And then to be sentenced on a coward's punch, intent is suddenly brought back, so how can it ever be used in that fashion? It has to change."

Australian Bureau of Statistics figures released this week estimate a quarter of Australian men have been assaulted by another male, at a rate of 600 incidents of violence every week. About 70 per cent of these assaults go unreported.

Anna O'Halloran, chief executive of anti-violence organisation Step Back Think, said millions of men had been affected by social violence, and that it was a problem too big to ignore.

"Overall, there has been a decline in men's experience of violence, but the job is not done. There are still too many lives cut short each year due to social violence," Ms O'Halloran said.

Attorney-General Martin Pakula said the state government would work with the Office of Public Prosecutions to determine whether the one-punch laws should be amended.

Prosecutors this year also withdrew an application for a judge to impose the mandatory term in the case of Richard Vincec, who killed Jaiden Walker with a single punch thrown outside Cherry Bar in Melbourne's CBD in May.

Vincec was later jailed for eight years after pleading guilty to manslaughter.

Mr Pakula said on Friday that in both the Lee and Vincec cases the OPP had determined the mandatory terms didn't apply because of the way the laws were drafted.

"We will work with the DPP to establish whether the law should be amended to broaden the circumstances in which prosecutors can seek to apply the statutory minimum," he said.

Since their son's death, the Cronin family has thrown its energy into establishing the Pat Cronin Foundation, which aims to eradicate social violence.

Matt Cronin said he and his family wanted to see the end of the coward's punch so no other families would suffer.. The foundation has organised a public walk on November 19, education sessions and a research project.

"Nineteen months ago a rusty dagger was thrust into our hearts and that dagger's been sitting there," Mr Cronin said.

"Today we're able to pull that dagger out, but there's still some rust there. There's a lot of healing; there's a hole in our hearts and we need to get that to heal."