The incident happened at 8pm on Wednesday while the officer was conducting inquiries at a Huntly address on an unrelated matter.
A police spokesperson said the officer had stepped out of his patrol car when he was struck.
A man was later arrested.
The spokesperson said the injured officer was expected to make a full recovery and was being supported through the process.
“The officer was transported to Waikato Hospital, assessed and treated for a moderate injury and discharged.”
Police Association president Chris Cahill said the incident highlighted the risk police officers faced when on duty.
Incidents of this nature were not common, he said.
Maryana Garcia is a Hamilton-based reporter covering breaking news in Waikato. She previously wrote for the Rotorua Daily Post and Bay of Plenty Times.