Camera footage from the Taser shows that the prisoner was not kicking out or in a position to assault the officers when both contact stuns were applied.
"Mr X was non-compliant and actively resisting the officers. They were justified in restraining him," said authority chair 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 suffered a rib fracture as a result of the struggle.
Police said the accepted the authority's findings.
Superintendent Bruce Bird, Waikato District Commander, said: "We have full confidence that our officer acted appropriately...and his actions were supported by other officers who assisted with restraining this prisoner."
Bird acknowledged also 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.
"Our staff face an array of challenges when dealing with aggressive members of the public and policing prisoners in court cells can be very challenging."
Bird said police had discussed this incident thoroughly with the officer involved and learnt from the mistake that was made.
