A teen who broke the jaw of an off-duty police officer and caused him a brain injury in a brutal attack will remain in jail after an appeal of his sentence was dismissed.

Blake Hollins-Apiata, 18, was jailed for two years and six months in June on a charge of wounding with intent to cause grievous bodily harm for an assault on Taranaki constable Tyson Young.

The teen's lawyer then launched an appeal of the sentence, arguing his client should have received home detention. But Justice Helen McQueen has since ruled the prison term was appropriate.

The events which led to Hollins-Apiata's incarceration played out on July 24 last year at a party on Battiscombe Tce in Waitara, north Taranaki.

Young attended while off-duty from his job as a police officer, while Hollins-Apiata and his friends were also guests.

Around 11.30pm the party was wrapping up and around 30 people moved out to the road.

A car arrived at the address and Young overheard Hollins-Apiata and his friends encouraging the driver to perform a skid.

Young, 26, tried to discourage this, warning them he was a police officer and that other officers lived nearby.

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The attack happened on Battiscombe Tce in Waitara. Photo / Tara Shaskey

A confrontation ensued and Hollins-Apiata threw a punch that connected with the right side of Young's jaw.

He lost his balance and fell to the ground, where he was then set upon by Hollins-Apiata and other members of the group.

The assault only came to an end when Young's friend intervened and dragged him away.

Moments later, Hollins-Apiata and his friends were overheard congratulating each other for "hitting a cop".

Young, a father-of-one, suffered two breaks to his jaw and a moderate brain injury.

He required surgery which saw two plates and eight screws inserted into both sides of his jaw. Then, due to complications post-surgery, he had a second procedure which removed the plates, screws and three teeth.

Young suffers ongoing neurological, psychological and emotional issues as a result of the assault.

He returned to work in March this year but on a gradual basis for only three hours, three days a week. It is unclear whether he will be able to return to frontline duty as a police officer.

Hollins-Apiata pleaded guilty to the offending and at his sentencing his lawyer Julian Hannam argued for a term of home detention.

But that wasn't to be for the teen and in sending him to prison, Judge Tony Greig said: "Police are there to protect the community, and they themselves must be protected otherwise they can't protect us."

Blake Hollins-Apiata appealed his jail sentence in the High Court. Photo / NZME

Hannam indicated immediately that his client would appeal the sentence.

That hearing was held in the High Court last month, during which Hannam was clear the purpose of the appeal was to achieve a sentence of two years or below so that home detention would become available.

He argued this would promote goals of rehabilitation and deterrence while avoiding imprisonment, where the teen would be "thrown into the arms" of other offenders.

Hannam submitted Judge Greig's starting point was excessive and that he should have given a larger discount for his client's youth.

The court should also take into account his lack of previous convictions and background factors such as Hollins-Apiata's "seriously recidivist biological father", Hannam told Justice Helen McQueen, who heard the appeal.

But Crown prosecutor Justin Marinovich opposed the appeal, arguing there was no error in the end sentence.

He said the starting point was not too high and the appropriate youth discount was applied.

Marinovich also contested the appropriateness of a discount for lack of previous convictions, given Hollins-Apiata's extended history in the Youth Court, and argued there was no clear nexus between his background and the offending to warrant a discount for cultural factors.

While Justice McQueen considered there was some connection, she ruled the "generous" 25 per cent discount given for youth was enough to account for both youth and cultural factors.

She also found Judge Greig did not err in assessing the starting point for the offending, and for not providing a separate discount for lack of previous convictions, her recently released decision detailed.

In declining the appeal, Justice McQueen said it was regretful that "this young man faces a not-insignificant period of imprisonment."

"However, in the circumstances, given the severity of the offending and the discounts afforded to the appellant, the sentence reached was within range and cannot be said to be manifestly excessive."