A police officer was unjustified in using a Taser on a prisoner, the Independent Police Conduct Authority has found.
Police said the prisoner was "abusive and threatening" while being moved at the Hamilton District Court on January 26 this year.
One police officer became so concerned that he drew his Taser but kept it hidden from the prisoner.
A struggle ensued when the prisoner was being escorted down the stairs, which ended with the officer using the Taser on the prisoner's upper thigh, quickly followed by a second contact stun.
Camera footage from the Taser shows the prisoner was not kicking out or in a position to assault the officers when he was Tasered.
"Mr X was non-compliant and actively resisting the officers. They were justified in restraining him," said authority chairman Judge Colin Doherty. "However, the authority is satisfied on the evidence that he was not assaulting or threatening the officers at the time he was Tasered.
"Mr X could and should have been restrained by the officers who were struggling with him, without the need to apply a contact stun. Other means to subdue him should have been used."
The authority was not able to substantiate an allegation that the prisoner was punched in the stairwell or had his head smashed against the loading bay wall.
The prisoner broke a rib in the struggle.
Waikato District commander Superintendent Bruce Bird he had "full confidence" the officer acted appropriately, and said his actions were supported by other officers who were helping restrain the prisoner.
Bird also acknowledged that the IPCA had deemed the force used on the prisoner at the security area was reasonable under the circumstances.
"We agree with the IPCA that the officer's use of Taser was contrary to policy and not justified because the prisoner was not directly assaulting or threatening him or others at the time," Bird said.
He said dealing with aggressive members of the public and policing prisoners in court cells could be very "challenging".
Bird said police had talked to the officer involved and learned from the mistake.