Police used unreasonable and excessive force when they tasered a 15-year-old who stole a tractor and led officers on a low-speed pursuit.
The youth said he was "shocked pretty good" by the police tactical weapon after the 19km chase which lasted 12 minutes.
In a ruling released today the Independent Police Conduct Authority blasted police for the way they handled the teen.
The watchdog said police breached policy which could have resulted in "unnecessary injury" to the young driver.
Shortly after midnight on April 16 last year the 15-year-old stole a tractor in Kaiwaka, damaging the garage of a local sports ground in the process.
Witnesses followed the tractor and alerted police.
The first officer to respond located the teen 13km away on State Highway 1.
She pulled in behind the tractor and the teen immediately began "pulling the fingers" and yelling at her.
She decided to wait for backup from other officers.
The teen then started driving the tractor onto the wrong side of the road, so the officer turned on her flashing lights and siren to signal him to stop.
The teen ignored her and appeared to become agitated.
She pursued the tractor and a second officer joined in his patrol car.
The tractor covered almost 19km from Kaiwaka to Wellsford in the hour from when it was first taken, to when it finally stopped.
The pursuit lasted 12 minutes.
During the pursuit the teen did several U-turns on the highway, frequently changing direction.
He often drove the tractor into the lane of oncoming traffic and turned off the tractor lights on several occasions - though the hazard lights were still operating.
The IPCA said there was "minimal road lighting between towns", but traffic was light, and the ground was dry.
The maximum speed the tractor reached during the pursuit was 18km/h.
The second officer managed to get ahead of the tractor and laid road spikes in a bid to stop the large vehicle.
The teenager drove around the spikes and carried on driving.
A third officer, aware of the pursuit, planned to lay further spikes in Wellsford.
As the teen attempted to avoid going over the road spikes there, he drove up on to the footpath towards the third officer.
He then stopped the tractor while keeping the engine running.
The third officer fired his Taser at the teen, who rolled off the tractor on to the ground.
He was then arrested.
The IPCA ruling revealed that the Taser's barbs had attached to the teen's clothing, rather than his flesh.
The teen said he was "shocked pretty good".
He was seen by a doctor afterwards, as required by police policy, but did not complain of any ill effects after being tasered.
Police investigated the incident and concluded the use of the Taser was "appropriate in the circumstances".
They identified two potential policy breaches which they considered minor.
IPCA chairman Judge Colin Doherty disagreed with the police.
"The authority found that it was not appropriate for the officer to fire the Taser in the circumstances, as the driver did not pose an immediate threat once the tractor had stopped and there were more appropriate actions the officer could have taken," he ruled.
"The Authority has found that [the officer's] use of his Taser was an unreasonable and excessive use of force in the circumstances.
"[The teenager] did not pose an immediate danger to [the third officer] or others at
the time the officer fired the Taser, and a less forceful tactical option could have been used to apprehend him."
The orange-coloured Kubota was stolen from a shed at the Kaiwaka Sports Association complex, where Mark Ottaway works as the groundsman.
In the early morning darkness Ottaway and his wife Pam had helped pursue the stolen tractor. Ottaway was driving while Pam, the passenger, was on the phone to police giving regular updates.
Waitemata Police District Commander Superintendent Naila Hassan said police accepted the findings of the IPCA's report.
But she offered explanation around the officer's decision.
"While we accept these findings, it's important to acknowledge that this was a dynamic, unpredictable situation, involving an intoxicated male driving dangerously on the highway and posing a safety risk to the public, himself and to our officers," she said.
"The nature of policing is unpredictable and our officers are frequently faced with situations where they are required to make split-second decisions in rapidly-changing, and often dangerous, environments.
"The officer involved in this incident was acting in good faith and with community safety at the forefront of his intentions as he attempted to resolve the situation with urgency, due to the considerable safety risk and danger posed to innocent motorists as a result of the dangerous driving by the intoxicated male on a main highway."
Hassan said police had taken on board the IPCA's findings and accept there were other tactical options available to the officer at the time.
"We will be communicating the lessons learnt from this incident to our people and the officer involved."