In April 2017, it was reported to police a man had assaulted someone in South Auckland.
When they arrived he was holding a premixed vodka drink and it was decided to arrest him for breaching his bail condition not to drink alcohol.
He was taken to the Counties Manukau District Custody Unit, where some police described him as "fooling around", according to the IPCA report.
A custody officer interpreted the man's behaviour as aggression.
While being escorted to a cell, the man struck the window of another cell with his hand.
The officer heard the strike behind him and decided the man needed to be controlled, according to the report.
In a bid to take control, the officer threw him into a wall where the man hit his head with some force.
CCTV footage showed him slide down the wall to the floor, seemingly unconscious as two officers tried to restrain him.
He was face down on the floor as the officers pulled his arms behind his back.
The IPCA ruled that in both of these incidents, excessive force was used.
The man refused the offer made by police for him to see a doctor.
"The man was eventually seen by a doctor who had been called into the custody unit to see another detainee," the IPCA report said.
"The doctor was made aware the man had been drinking alcohol, but was not told that the man may have suffered a head injury."
The IPCA ruled police should have called a doctor regardless of the man's wishes.
Authority Chair Judge Colin Doherty said the force against this man "was unnecessary and excessive".
"Custody staff ought to have reassessed the man's health after he was injured, and increased their monitoring of him until he was seen by a doctor."
The IPCA has recommended that police provide relevant CCTV footage to health professionals who are called to examine detainees.
Counties Manukau District Commander Superintendent Jill Rogers said police accepted the findings.
"As police we acknowledge that we have a duty of care for people that are held in the custody unit," Rogers said.
"We set high standards for our staff and we strive to deliver on those every day.
"We acknowledge in this case the actions of this officer were excessive and we have taken appropriate action as a result."