The police watchdog has found the tasering of a drunk teenager driving a stolen tractor was an excessive use of force.
The 15-year-old was pursued by two police officers after stealing a small tractor from a Kaiwaka sports grounds and driving it to Wellsford on 16 April, 2018.
An officer first spotted the teenager on State Highway 1 and followed him but he began "pulling the fingers" and yelling at her, an Independent Police Conduct Authority (IPCA) report reads.
The driver then began driving the tractor on the wrong side of the road and, joined by a second officer, he was pursued by police.
Travelling at a maximum speed of 18 km/h, the tractor covered almost 19 kilometres from Kaiwaka to Wellsford from the point it was stolen.
In the pursuit, which lasted 12 minutes, the teenager drove on the wrong side of the road, changed directions several times and turned the lights on and off.
The teenager eventually drove onto a footpath to avoid a set of road spikes set up by a third officer and stopped the tractor but kept the engine running.
He was tasered by a police officer and rolled off the tractor and onto the road before being arrested.
The taser barbs attached to the teenagers clothing but he said he was "shocked pretty good".
Police investigated the tasering themselves and despite identifying two potential policy breaches they found the officer's decision to use the taser was appropriate.
A separate investigation was carried out by the IPCA who found the tasering unreasonable and an excessive use of force.
The officers had told the police watchdog they believed the teenager, one officer described as "highly unpredictable", posed a real risk and may be trying to ram a police car parked next to the spikes.
But the IPCA found the driver did not pose a threat and the tasering could have resulted in unnecessary injury to the teenager.
It pointed to police policy, which states tasers should not be used on people operating machinery and that they pose a greater risk when someone is intoxicated.
Waitematā District commander superintendent Naila Hassan accepted the findings but said the police officer was acting in good faith with community safety at the forefront of his intentions.
"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 Police officers.
"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."
She said it was accepted the police officer had other tactical options and lessons learnt from the incident would be communicated to the police workforce.