The woman had not attended the party and was looking for her son, who had called her in distress.
Police also failed to provide one of the people they arrested with a blanket and a phone call while in custody.
Waikato district commander Superintendent Bruce Bird said police who attended the parties received physical and verbal abuse from a large number of intoxicated people.
"In both instances police had the consent of the occupier to close down the parties and we did so in accordance with our policy around out-of-control gatherings," Mr Bird said.
"In these tense situations we don't always get it right and we accept the IPCA findings in relation to the use of force used by one of my officers, and the failure to provide a blanket and a phone call to a person in custody.
"We acknowledge that we made errors but overall, given the complexity of the challenge of managing these volatile situations driven by alcohol, I'm pleased that my staff once again demonstrated high levels of professionalism."