A police officer used excessive force during an arrest at a large party in Huntly, the Independent Police Conduct Authority (IPCA) has found.
Two officers called for back-up when they came across a house party which had spilled onto the road, in November 2017.
About 50 partygoers swore, shouted abuse and threw glass bottles at the officers as they tried to disperse the crowd.
About 10 people ran down a nearby alleyway in an attempt to escape but three were arrested.
The authority has found one of the officers unjustifiably used knee strikes during the arrest.
It said it also "determined that this officer made concerning comments about his actions during the incident to a colleague, including a comment to the effect that "it's about time some of these kids got what they deserved".
Police returned to the party later in the night where a crowd was gathering again.
As police approached, two men and a woman remained, one of the men holding a screwdriver.
An officer drew his baton and struck the man in the torso.
The Authority accepted that the officer believed the man could have caused significant harm and found that he was justified in striking the man in defence of himself and his colleagues.
IPCA general manager Warren Young said the 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," he said.
The police have accepted the findings, and say a separate investigation found there was insufficient evidence to prosecute any officers involved.
Police also said they "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".