The remaining 10 people ran down an alleyway in a bid to escape police, who gave chase and made three arrests.
An officer later said that he saw his colleagues use excessive force during an arrest in which police had pulled one male from a bush and forced him to the ground.
In the report the concerned officer told the IPCA they were "beating the ***t out of him basically", landing blows that included "elbow strikes, knee strikes, kicks, and punches" while the male was screaming, he said.
The accused officer said the allegation was an "absolute fabrication".
However, the IPCA ruled using knee strikes during the arrest was unjustified in the circumstances.
The IPCA also ruled that this officer made concerning comments to a colleague, including a comment to the effect of "it's about time some of these kids got what they deserved".
About 1.30am, four officers returned to Semple St, where they saw another crowd gathering.
As police approached, the group dispersed, apart from two men and a woman. One of the men was holding a screwdriver. An officer drew his baton and struck the man in the torso.
The IPCA accepted that the officer believed the man could have caused significant harm and found that he was justified in striking this man in defence of himself and his colleagues.
IPCA general manager Warren Young said this incident came to light through a complaint by an attending officer.
"The authority commends the officer for raising his concerns about the actions and comments of his colleagues."
Waikato District Commander acting Superintendent Warwick Morehu said police accepted the findings that an officer used excessive force during an arrest in Huntly.
"Police acknowledge the attending officers brought a difficult situation to order," Morehu said.
"An officer involved in the dispersal later came forward to express concerns about the conduct of some others during the operation.
"This matter has been the subject of robust police and IPCA investigations, which were run separately."
Police's investigation and subsequent legal advice found there was insufficient evidence to prosecute any officers involved, he said.
Based on that information, the matter has been closed.
"The IPCA report highlighted that a number of use of force reports from that incident were not submitted as per New Zealand Police policy," he said.
This issue was raised with the officers involved, he said.
"Police would like to commend the actions of the officer who did the right thing and spoke up when he believed he had seen concerning behaviour from colleagues."
