However, the organisation's watchdog has ruled he took things too far after that and should have stopped hitting the man about 30 seconds into a struggle which lasted for a minute and 40 seconds.
The man was arrested for breaching his bail conditions and put into a holding cell at the Christchurch Central police station at 11.20pm on June 4, 2020.
He was intoxicated, belligerent, had a cut on his foot and didn't want to move cells as was requested of him by one of the police officers.
At about 12.30am the officer spoke to the man through the cell door, explaining why he needed to move cells but the man stood up and paced around before standing about half a metre away from the officer.
The officer says he believed the man was about to attack him, so he stepped forward and pulled him to the ground to avoid this.
During the ensuing scuffle the prisoner grabbed the officer's testicles and squeezed them tightly at least four times - which resulted in the officer striking him to the head multiple times with his forearm or closed fist.
Four other officers came to help restrain the prisoner - one of whom stood on his buttocks - but the officer continued to hit him several more times and applied pressure to his throat using his forearm.
The man was eventually put in handcuffs before being transferred to another cell.
A complaint was made by the man to the Independent Police Conduct Authority, on October 30, alleging he was repeatedly assaulted during the incident by being thrown to the ground, punched, kneed, elbowed, and held by the throat.
After viewing CCTV footage of the incident the prisoner claimed he was worried about where the punches were hitting him as "[being hit in] those areas can kill people."
The IPCA's findings, released on Tuesday, found overall the officer's use of force was justified but he should not have struck the defendant's head or applied pressure to his neck during the struggle.
"We accept that Officer A acted, in part, to overcome Mr X's threat of violence to resist his removal from the cell, and that Officer A reasonably believed that Mr X's resistance was to prevent police from carrying out this action."
However, the authority found that the following blows targeting the man's head and neck, causing it to hit the concrete floor, were not condoned and neither were the actions of another officer who stood on the prisoner's buttocks.
CCTV footage showed there were bloody footprints and smears covering the floor, bench and wall of the cell and the officer told the authority the prisoner was obstructive, swore at him and told him: "… you can clean up after me, you little bitch".
The officer said when the prisoner jumped up off the bench and challenged him he believed he was about to be assaulted and needed to act quickly.
He took the man down using the back of his head to allow other officers to pull him into a three-man takedown, believing there was not time to back out of the cell and close the door before he was attacked.
Other officers described the man as very strong, unco-operative and difficult to restrain.
The authority ruled the strikes to the prisoner's head causing it to hit the floor and the officer's use of his forearm to put pressure on the man's neck were not warranted.
"We do not accept Officer A's explanation that he had no other options available to him in the circumstances, or that he mistook Mr X's neck area for his torso.
"Officer A uses a level of force beyond what is required to protect himself, his colleagues and restrain Mr X. The force appears to be motivated by anger."
Standing on the man's buttock's was dangerous and served no purpose, it said.
While the authority accepted the prisoner had been declined medical treatment for the cut to his foot, which he suffered before being arrested, it ruled a doctor should have been called after the scuffle given he had receiving the blows to his head.
In March 2022, Canterbury Police District circulated a directive detailing the process for dealing with an individual who had suffered blows to the head.
"If a person taken into Police custody has immediately prior to, during or after their arrest received one or more heavy blows/strikes to the head area, a health professional must be consulted to assess the need for any additional medical intervention and care."
Police acknowledged the IPCA's findings.
Canterbury District Commander Superintendent John Price said steps had been taken to avoid similar situations in the future.
"It is always unfortunate when police find themselves in circumstances where they must resort to using force," Price said.
-By Leighton Keith
Open Justice multimedia journalist
