A 30-year-old man allegedly assaulted a special-duty police officer trying to break up an argument at the Ewa Beach Zippy’s Saturday morning.

Police said the officer was working at the Zippy’s restaurant at 91-1669 Fort Weaver Road, when he tried to break up an argument at the counter between two groups of men at about 4 a.m.

When the officer was between the two groups, the alleged assailant punched the officer in the mouth, police said.

The officer detained the man and kept the two groups from fighting until more officers arrived.

Police arrested the suspect for investigation of first-degree assault on a police officer. The officer went to the hospital for a chipped tooth and was released, police said.