A police officer should not have punched a woman's face after she bit him last year, the watchdog has ruled.
It also found the bleeding woman did not receive appropriate medical care while she was in police custody.
In April 2022, the woman was arrested in Auckland for a breach of her bail conditions and was handcuffed in the back of a patrol car.
She tried to escape and was stopped by the officer, biting his left forearm in the process. This prompted the officer to punch her in the face.
A review from the Independent Police Conduct Authority (IPCA) found the force used by the officer was unreasonable as he had other, less forceful options available to him.
It believed the closed fist punch was not the best course of action, as officers were trained to stop assaults using less force.
The officer said the punch was an intentional act in self-defence.
"However, he says he was scared, and his punch was an instinctive, reflex reaction to immediately stop her from continuing to bite him. He says the punch was not intended to be 'malicious' and was not a retaliation for being bitten," the report read.
The officer said that he needed to act decisively to stop injury to himself, and he did not believe a push would suffice.
ICPA chairperson Judge Kenneth Johnston KC said the officer could have used an open palm strike, which is a tactic officers are trained in.
"In this case, the test for the reasonableness of the force used was finely balanced; we applied our minds to the tactics officers are taught and found that the force the officer used, was ultimately unreasonable because he could have used the less violent option of an open palm strike to stop the assault."
The woman told IPCA that after her release from police custody, she went to Auckland City Hospital where a doctor recorded that she had a cut above her left eye and bruising to the surrounding tissues.
The review found the woman was not afforded appropriate medical care while she was in police custody.
"It is clear from the custody footage, when [the woman] was received and processed at the Auckland custody unit, she had blood visible on the left side of her head.
"Because she suffered a head injury, policy required custody staff to call a doctor to examine the woman, which they did not do."
The report also found that the woman's injuries were not appropriately recorded or photographed.
"No photographs were taken of [the woman's] injuries. [The officer] agreed this should have been done but [he] says that it was not something he thought of at the time.
"[The officer] also did not think it would be appropriate for him, as the officer who used the force, to take photographs of [the woman's] injury, as she was upset and would likely be uncooperative."
It said documenting the woman's injuries should have occurred as part of police's evidence gathering process.
"The use of force by a police officer may at any time become the subject of an investigation. As such, all available evidence should be gathered in a professional and unbiased manner.
"In addition to not photographing the injuries, her custody evaluation failed adequately to record her injuries; this, notwithstanding the presence of visible injuries in the custody footage."
The IPCA report recommended that police develop guidelines for appropriate staff to photograph injuries caused to both officers and people because of police actions taken.
Acting Superintendent and relieving Auckland City District Commander Sunny Patel said police acknowledged the IPCA's findings into the incident.
"Police acknowledge the IPCA's findings that the use of force by the officer during the arrest was not reasonable in this case," he said.
Patel said police also acknowledged the findings around the care the woman received following the incident and the documentation of her injuries.
"We place high expectations on all of our employees across the organisation and as a result an employment process was carried out."
Patel said police were looking to refresh training for staff around appropriately documenting a person's injuries.
The officer involved remained an employee of New Zealand Police.