Aaron Dusmanovic and the victim, a resident of Western Australia who was in the Illawarra for work, had both spent the evening of May 16 at Hotel Illawarra and were among the last to leave the premises sometime after 3 o'clock the next morning.

The victim approached Dusmanovic's group a short distance away from the pub, believing these had been the people he'd been drinking with.

He later told police he saw some of the men in the group get into a fight and he tried, unsuccessfully, to intervene.

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He said he then walked off and was unaware Dusmanovic had followed him. CCTV footage of the incident shows the 25-year-old approach the victim from behind and punch him to the right side of his head.

The blow caused the victim to fall face-down on the roadway, unconscious, where he remained for several minutes, not moving.

Dusmanovic and his friends left the man blacked out on the roadway and walked off without offering any assistance.

Only one man stayed behind to help, rolling the victim onto his back and attempting to revive him while contacting emergency services.

The victim was taken to hospital but was still "largely incoherent" when speaking to police. They photographed the man's visible injuries - swelling and grazing to the left cheek, lacerations to the lower lip and several loose teeth.

Doctors also confirmed the victim had a fractured nose.

Dusmanovic was arrested just before 10pm that night.

In an interview with police, he said the victim approached his group and began hassling them before trying to pick a fight with one of his friends.

He claimed the man called one of his female friends a slut, prompting one person in the group to push him onto the road.

Dusmanovic admitted he followed the victim, punched him in the jaw and saw him fall down.

He was charged with affray, to which he subsequently pleaded guilty.

The court ordered a background report ahead of Dusmanovic's sentencing in August.