The career of a young Auckland cop hangs in the balance after he was today convicted for illegally presenting a Taser at a woman.

Constable Sean Mathew Doak faced two charges related to wielding a Taser but was acquitted of one after a trial in August.

The jury found the 25-year-old not guilty of assault with a weapon but guilty of unlawfully presenting a restricted weapon.

In the Waitakere District Court this afternoon, his lawyer Todd Simmonds continued to argue for a discharge without conviction after his client's sentencing was adjourned part-heard.

Simmonds said affidavit evidence from the senior legal officer for the NZ Police Association showed Doak would "more likely than not" lose his job if convicted of a weapons offence.

"His employment will be terminated if a conviction is entered in this case," Simmonds said.

Doak was found guilty of briefly firing the Taser's arc mode without cause towards an apprehended and handcuffed woman in the back of a police car.

The arc option triggers the Taser to produce an electrical current between two prongs.

Judge Noel Sainsbury said New Zealanders "expect better" from their police officers.

"That needs to in my view be marked with a conviction because of the particular role and trust we have in police officers.

"He may well need to learn from this and he may well need further training. It was a poor piece of decision-making."

He said a conviction was not out of proportion to the gravity of offending.

"As a community we put high levels of trust in our police, we give them a high level of power over other citizens," the judge said.

"When police have the ability in appropriate circumstances to use serious force we trust them to do so responsibility."

But Judge Sainsbury continued: "We don't expect, and it's not reasonable to expect perfection. People make mistakes."

He said a conviction was not intended as a statement that Doak should not be a police officer, but rather statement that police officers will be subject to the law like everyone else.

The judge was also unconvinced it was a certainty Doak would lose his job due.

"That's a decision for the [Police] Commissioner," he earlier said.

"That doesn't mean he can't be a good police officer, because people learn from mistakes."

The allegations against Doak came after a high-speed pursuit during the early hours of September 17, 2017.

The chase began in Mt Eden, with the fleeing driver in a white Subaru potentially reaching speeds of up to 200km/h, the court heard.

Police were forced to call off its ground units, while the Eagle helicopter tracked the suspect car to the underground carpark of Auckland's downtown casino.

The driver quickly bolted from the scene, leaving 23-year-old Mary Jane Takerei in the passenger seat.

Doak and his partner, Constable Florence Roberts, were the first officers on the scene.

Takerei told the court that Doak pepper sprayed her before she was dragged away by police holding her ankles.

Multiple police officers, however, also said Takerei sprayed Roberts in the face with what appeared to be a can of CRC.

After searching for the driver, Doak returned to Takerei - who was by now surrounded by police officers.

CCTV footage of the incident shows Doak kneeled down beside her with his Taser drawn as she lay on the ground.

Judge Sainsbury said it appeared Doak was attempting to gather information from Takerei about the driver in a "robust" way and in difficult circumstances.

Takerei claimed the constable may have pressed his Taser on her forehead between her eyes - leading to the assault charge.

"What's his f**king name, I swear to God I'll f**king Taser you," she claimed Doak yelled at her.

The video footage shows Takerei's legs flailing.

However, other police officers at the scene, including Roberts, told the court they didn't hear Doak threatening Takerei with his Taser or see him pressing it against her forehead.

The jury agreed with them and found Doak not guilty of the assault with a weapon charge.

The constable was later accused of presenting the Taser and firing the arc mode towards Takerei in the back of a police car as he and Roberts attempted to transport her home.

A recording from the weapon showed the arc mode was activated briefly but Takerei was not shocked at any stage.

She offered no evidence during the trial about the arc incident.

Judge Sainsbury said it was understandable that Doak was frustrated and angry with Takerei at a time when his adrenaline was flowing.

But the judge continued Doak made a "very poor decision to go into the car and allow his Taser to both spark and make the noise, as a way of letting her know how unhappy he was with her that night".

"What needs to be made clear though is this did not go any further, he did not lay a finger on her."

Simmonds has said the arcing was fleeting.

"That may well explain why Ms Takerei appeared to not even notice the Taser," he added.

Takerei was arrested for assaulting Roberts after slamming a car door against the officer's leg, while the wanted driver was later found by police leaving an elevator in the casino.

Judge Sainsbury said it doesn't appear Doak's offending had an affect on Takerei, "although that may be more luck than anything else".