As an off-duty police officer lay battered and concussed on the side of the road, a proud Blake Hollins-Apiata shook hands with his mate who congratulated him and said "you just hit a cop".

Only metres from the teens basking in their misguided glory, constable Tyson Young was suffering a broken jaw and a head injury so bad that his "dream job" of being an officer on the frontline remains in jeopardy.

Nearly a year on from the attack, Young's slow and painful recovery continues and Hollins-Apiata's puffed-up bravado has now been replaced with fear.

On a charge of wounding with intent to cause grievous bodily harm, the 18-year-old was jailed for two years and six months this week - a sentence the New Plymouth District Court heard would be a "purely destructive" outcome for the Taranaki teen.

His friends who were also involved were dealt with in the Youth Court.

Hollins-Apiata appeared shaken when he learned of his fate and he fought back tears. His mother wept in the gallery, and his father quickly approached him to offer a few words through the glass partition.

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

Young is a relative of the host, who was celebrating her 18th birthday, and attended the party 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.

Hollins-Apiata, then 17, and his friends approached a vehicle and encouraged the driver to perform a skid outside the front of the property, where people were congregating.

Young overheard this and discouraged the group, warning them he is a police officer and that other officers lived nearby.

The group told Young they didn't "give a f***" that he was an officer.

The assault occurred on Battiscombe Tce in Waitara, north Taranaki, in July last year. Photo / Tara Shaskey

According to the agreed summary of facts, Hollins-Apiata then threw a punch at Young, connecting with his jaw and causing him to stagger and fall to the ground.

A group of teens, including Hollins-Apiata, then continued to assault him as he lay injured.

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

Moments later, Hollins-Apiata was overheard speaking to his friend.

"[They] congratulated one another saying 'you just hit a cop' and proudly shook hands with each other," the summary detailed.

New Zealand Police reported this year that assaults on officers are on the rise, with 2633 reported nationwide in the last five years.

Life has changed dramatically for Young, a 26-year-old father-of-one, since the incident.

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.

Blake Hollins-Apiata was jailed when he appeared in New Plymouth District Court this week. Photo / Tara Shaskey

As a result, he now endures numbing to his face and tongue and at times slurred speech.

He also suffers memory loss, severe headaches, vertigo, lack of energy, loss of balance, and slowed reactions.

The ongoing neurological, psychological and emotional issues have put a strain on his family and after nine months off work, financial pressures have also taken a toll.

Young returned to work in March this year but on a gradual basis for only three hours, three days a week.

"His dream job of being an officer on the frontline is now in jeopardy. He may never be able to return to those duties due to the ongoing symptoms," Judge Tony Greig told Hollins-Apiata at his sentencing.

"That is the harm that you have caused".

The teen told the court he never intended to cause the pain and suffering that he has when he assaulted Young that night.

Defence lawyer Julian Hannam said it was a result of Hollins-Apiata's immaturity and poor-decision making coupled with alcohol, a group environment and aggression between parties.

A "personality transformation" occurs when he consumes alcohol and he is unable to regulate his response, Hannam said of his client, adding it was an issue Hollins-Apiata was keen to address.

He implored the court to step back from imprisoning the teen.

"Prison would be a purely destructive sentence to impose upon an 18-year-old who offended while he was 17."

Hollins-Apiata had a taste of jail when he was remanded into custody for a time, and while he entered with a degree of "immature bravado", that quickly dissolved and he never wanted to return, Hannam said.

Crown prosecutor Jacob Bourke said the attack was targeted and had caused a serious injury.

He suggested a start point of five years' imprisonment, much higher than defence's three years and six months.

Bourke accepted a discount should be allowed for Hollins-Apiata's youth, but submitted 10 to 15 per cent was more appropriate than defence's suggestion of 30 per cent, given he had previously been dealt with in the Youth Court and had not taken advantage of the opportunities that arose from those proceedings.

Judge Greig took a start point of five years and applied a 25 per cent discount for Hollins-Apiata's guilty plea and 25 per cent for his youth.

Sentencing the teen to two years and six months' jail, Judge Greig said he had to hold him accountable for the harm he had caused, denounce his conduct, deter others and protect the community.

"Police are there to protect the community, and they themselves must be protected otherwise they can't protect us. The community needs protecting."

After the hearing, Hannam said he had been instructed by his client to appeal against the sentence.

Young has not responded to Open Justice's request for an interview.

- Tara Shaskey, Open Justice