The police watchdog says an officer should have been charged after they kicked and punched a man lying on the ground during an arrest in Auckland last year.
The man had tried to run over officers in the driveway of a house after they were called to a family harm incident.
The Independent Police Conduct Authority (IPCA) said the arrest was captured on CCTV footage.
It showed the man getting out of his car after a short chase and lying face down with his hands behind his head.
The officer then stood on the man's head, kicked him several times in the body and punched him in the head before he was handcuffed and arrested.
The IPCA said the officer's report on the incident did not accurately reflect the amount of force he used.
The officer had said he had kicked the man twice but the video showed he kicked the man four times.
The officer also said the man had approached him with clenched fists and his chest pressed out, but the video showed the man was compliant and immediately surrendered after getting out of the car.
The IPCA said the officer's behaviour was not motivated by the perception of risk but was retaliation for the man trying to run the officers over.
It said the police found the officer's use of force was excessive but decided not to charge him with a criminal offence as they did not believe it was in the public interest to do so.
But the IPCA said the officer used deliberate and gratuitous force and should have been charged.
It also disagreed with the police view that a prosecution was not "winnable".
'This was a fast-paced, unpredictable and dangerous situation' - police
The police said in a statement they were correct not to press charges given the circumstances.
Superintendent Karyn Malthus said there was not enough evidence for a conviction to be likely.
She said the police decided the public interest test in the Solicitor-General's prosecution guidelines was not met.
"This was a fast-paced, unpredictable and dangerous situation where our attending officers were dealing with an offender who moments ago attempted to run them over before fleeing the scene," Malthus said.
The officer was in a heightened state of emotion which undoubtedly impaired his judgement and decision-making, she said.
"Police accept the officer's explanation that they believed the risk posed by the offender remained high.
"Having reviewed this incident and hearing the explanations of the officers involved, I believe there was no intent by the officer to cause harm on the offender, who was not injured, and instead the officer's actions were designed to achieve compliance by the offender so he could be handcuffed.
"We do accept the officer did not handle the situation appropriately and made a number of tactical errors and exercised poor judgement during the arrest."
The police said employment action has been taken against the officer who remains on the force.