Matthew Egan, 30, had been staying at the Castlereagh Hotel in Dubbo with his friend, when the incident occurred about 1.35am on July 16.

Police were conducting patrols on Brisbane Street for an unrelated steal from motor vehicle incident when they witnessed Egan throw a closed fisted punch at his male friend's face.

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Officers stopped and separated the two and placed Egan on the ground before handcuffing him.

The victim had swelling around his left eye and black colouring around the outside of his eye. There was also a large lump under the eye and blood on his face.

Police called an ambulance which attended and treated the victim at the scene.

Egan told the officers "I just swatted a f---ing big mozzy that was on his face".

He was arrested and taken to Dubbo Police Station, where according to police Egan was "belligerent and argumentative" toward officers.

According to court documents at the time of the attack, Egan had been on conditional bail to be of good behaviour for another incident involving domestic-violence related chocking and malicious damage.

Appearing via video link from custody, Egan pleaded guilty to assault occasioning actual bodily harm and behaving in an offensive manner in a public place in Dubbo Local Court on Wednesday.

In court documents police said Egan seemed to have a problem with alcohol and "commits offences when intoxicated".

Defence lawyer David Hemsworth said Egan had engaged in "inappropriate lashing out", and had expressed to him he was an alcoholic and hoped to engage with drug and alcohol counselling.

Magistrate Theresa Hamilton convicted and sentenced Egan to a 15-month community corrections order.