A man who played a part in a street fight that ultimately killed MMA fighter Fau Vake last year says he is ashamed and sorry for the attack on "another Tongan brother".

Siofilisi Paongo, 31, is not responsible for the fatal assault but swung multiple punches at Vake's brother James Ika Vake when he was on the ground.

Attacking a man in a vulnerable position was one of three aggravating factors Justice Sally Fitzgerald raised at Paongo's sentencing at the Auckland High Court Tuesday morning.

Fau, whose full name was Lifau Tu'iha'aingana Vake, was known for training alongside New Zealand's top martial arts fighters at City Kickboxing.

He and his brother James were on Auckland's Symonds St in the early hours of May 16 last year when they were assaulted by Paongo and three others.

Justice Fitzgerald said it is not known how the fight started but the tragic consequences of the fight - lasting only three minutes - are clear.

One of Paongo's friends, Daniel Havili, punched Fau squarely in the face, making him fall backwards, hitting his head on the pavement. The impact caused a brain bleed and Fau died in hospital nine days later.

"I make it clear however, that you were not at all involved in the assault on him," Fitzgerald said to Paongo, whose two assault charges related to James.

During the fracas, one of the men pushed James so hard against the doors of a barber shop that the lock broke, he fell through the doors and into the shop.

Reading from court documents, Justice Fitzgerald said Paongo, who was not involved until this point, approached James when he was still on the ground, grabbed his clothes with one hand and swung two punches at his upper body.

One punch grazed James' back and the second connected with his left side around the rib cage.

James remained on the ground in a kneeling guarded position, and Paongo punched him again, once to the body and twice to the head.

Someone then pulled Paongo out of the barber shop, allowing James to run out to Symonds St. Paongo followed and punched him in the head again.

James suffered a concussion, bruises, cuts and abrasions, said Justice Fitzgerald, listing three aggravating factors - Paongo delivered three punches to James' head, acted together with associates, and attacked James when he was vulnerable and on the ground.

The offence was not the most serious of its kind but there were no mitigating factors, she said. "Being drunk is no excuse."

Paongo's cultural report showed he was one of 11 children raised in a humble and happy home in Tonga by parents who provided him with "the best they could", Fitzgerald said.

He left high school at 17 to enlist in the Tongan army and was sent on various peacekeeping missions including to Afghanistan and the Pacific over his five-year service.

He came to New Zealand in 2013 to earn better money and currently works as assistant supervisor at a tunneling company.

Paongo continues to provide for his brother's two children, who lost their father to suicide.

"I am ashamed of the way I acted towards another Tongan brother. I don't expect my apology to be accepted but I am truly really sorry," he had told the probation officer who wrote his pre-sentence report. "I can't imagine what the victim's family is going through."

"I can't change the past but I can change the future by how I act. This will not happen again, my deepest condolences to the family for their loss. I wish I never took part," he said.

Justice Fitzgerald sentenced Paongo to five months home detention with a curfew on his non-work hours - 7pm to 5.30am when he is on the day shift, and 6.30am to 6pm when he is on night shift.

The sentence includes a 15 per cent credit for his remorse and 20 per cent for his guilty plea, which spared the victims and family the distress of going to trial, the judge said.