Police in Waikato are interviewing a man about an attack on an officer in Ngaruawahia.
The officer was left bleeding and unconscious in Newtown Street on Wednesday night after going to the aid of a woman he believed was being assaulted.
Police say the officer got out of his patrol car to speak to a man and appears to have been hit.
He was admitted to Waikato Hospital but later discharged to recuperate at home.
Police say a man was located at a house a short distance from where the attack took place and is being questioned on Thursday.
The Police Association says the public cannot continue to expect officers to enter dangerous situations when they have no way of arming themselves.
Association president Greg O'Connor says it is extremely unlikely the officer would have been injured if he had been able to draw a firearm or a taser stun gun before confronting the offender.