Detective Senior Sergeant John Sutton said two other men were interviewed and released, and received formal warnings for fighting.
The officer used his police radio to call for help. Two members of the public also came to his aid.
"We're grateful that he was assisted by two members of the public and that police were able to respond quickly to this call for help,'' Mr Sutton said.
"The welfare of our staff is important to us and we are working to support him, his colleague and all staff in our district. Police should not be subject to any kind of physical violence while in the role of protecting the community.''