Justin Marshall's attacker is son of Black Widow killer Helen Milner

The man found guilty of punching and stomping on former All Black Justin Marshall outside of a Queenstown bar is the son of Black Widow killer Helen Milner.

Adam Kearns, 23, was sentenced at Invercargill District Court this morning to a period of four months' home detention and 250 hours of community work after he was earlier found guilty by jury of assault with intent to injure.

The assault, described by Judge Michael Turner as "unprovoked, alcohol-fuelled street violence", came after Kearns and Marshall had both been inside a Queenstown bar drinking in separate groups into the early hours of Good Friday last year.

Kearns claimed that Marshall picked up his beer and drank from it. He remonstrated with the former rugby player who either didn't hear him or ignored him, the trial heard.

Once they left, they had words on Shotover St with Kearns telling Marshall: "You think you're the f****** man, well, you're not."

A scuffle broke out and Kearns and his mate, Tai Samuel Neilson, 25, who last year was sentenced to five months' home detention for his role in the assault, started attacking Marshall.

Both men were then seen on CCTV footage punching, kicking, and stomping on the 81-Test halfback and SKY Sports rugby commentator while he was on the ground.

The trial heard that Marshall had curled up to protect himself from the blows.

Marshall's attacker Adam Kearns (pictured) also suffered injuries in the Easter Weekend incident. Photo / Supplied

The assault ended when a female motorist saw the incident, stopped her car, and confronted Kearns and Neilson.

Marshall suffered bad bruising to the back, head and body, as well as lacerations, and a large contusion under the left eye.

In his victim impact statement, Marshall said he now feels "vulnerable" in public and when walking in crowds.

The publicity after the incident had an effect on him and his family, Marshall said.

Kearns narrowly escaped a jail term earlier this year after he was caught dealing cannabis and in possession of a gun.

He told police he had the cut-down single-barrelled sawn-off shotgun because his mother Milner, who is serving a life sentence for the murder of her second husband Phil Nisbet, had wanted him killed.

"My old lady is paying for a hit to be put on me," he said.

In April, Kearns was sentenced to eight months' of home detention, 150 hours of community work, and ordered to undertake psychological assistance.

Today, Crown prosecutor Mary-Jane Thomas said home detention was again "on the cards".

Defence counsel Alister James agreed, adding that Kearns has good support in the community and from his landlord.

"Mr Kearns a year or so ago had some difficulties in his circumstances but I think he is addressing those," Mr James said.

Marshall's injuries "in the scheme of things" were relatively minor, the lawyer said.

Any concern Marshall had with the media publicity caused by the incident came because he was "partly embarrassed", Mr James said.

During his trial, Kearns claimed he was acting in self defence after Marshall had attacked him.

Judge Turner described the assault as "unprovoked, alcohol-fuelled street violence".

He noted that Kearns had changed his circle of friends and gave him some discount for personal factors, relating to his upbringing and his mother's murder trial.

But the judge said though Kearns was entitled to some sympathy, it was not something he could "continue to trade upon from this point on", and sentenced him to four months' of home detention and 250 hours of community work.

Six months of special conditions was built into the sentence to allow Kearns to undergo anger management treatment and psychological assessment.

Kearns' testimony helped convict his mother of fatally poisoning Mr Nisbet in 2009.

He later won $55,000 from his killer mum after she had framed him and put him behind bars. Milner had admitted perverting the course of justice and was jailed for two years and eight months when she sent herself death threats and claimed they were from her son.

Kearns was arrested over the alleged threats and spent 18 days in custody, including his 19th birthday, while it is alleged that police took 13 days to carry out a search warrant which would eventually clear his name.

He has also launched legal action against police for allegedly failing to properly investigate his case.