But apparent town loyalties quickly dissolved when the other local turned on him in the wee hours at Dapto railway station.

Tylan Brown, 20, bashed the 18-year-old man unconscious, only moments after he'd been ready to join his victim in a fight against a rival group of out-of-towners.

Port Kembla Local Court heard the vicious attack, in which Brown repeatedly punched and kicked the man in the head, and - when he was unconscious on the ground - twice stomped on his head, left the teen lying in a pool of his own blood.

Miraculously, the boy escaped with only minor injuries.

In court on Friday, Magistrate Michael Stoddart jailed Brown for a minimum of 12 months, labelling him a "callous coward".

"You kicked him in the head four times, and when he was lying on the footpath you stomped twice on his head," Magistrate Stoddart said, recalling the horrific details of the case.

"What a gutless attack.

"You're lucky you're not here on more serious charges, this could have been fatal.

"There's only one place for you Mr Brown and that's jail."

Police documents tendered to the court said the victim was highly intoxicated on the night of September 27 last year after attending a party at the Ribbonwood Centre in Dapto.

After leaving the centre, he and friends headed to a nearby kebab shop, where the victim got into an argument with a group of men.

A short time later both of the groups turned up at the train station.

The victim approached one of the visiting group and, without warning, punched him in the face. The pair then got into a scuffle.

The court heard Brown, who was with the victim's group but said he did not know the teen, positioned himself near the boy so he could "jump in" and assist him in the fight if required.

However, a few moments later the teen turned on Brown and punched him in the face.

Brown retaliated by punching the victim three times, knocking him to the ground.

He was then joined by a mate, and the duo repeatedly kicked the victim in the head.

Police said CCTV footage of the incident clearly showed the second kick delivered by Brown knocked the teen unconscious, and he slumped to the ground.

However, both men kicked the boy twice more, before Brown raised his right leg and stomped on the teen's head twice.

Bystanders quickly pulled the pair away from the motionless teen at the same time that police pulled up, scattering the crowd.

Officers chased Brown, who was seen running away from the bleeding victim.

He was apprehended several hundred metres away and returned to the scene.

When questioned, he said to police: "I was going to help a fellow Dapto boy out 'cause he was fighting with a group of Shellharbour boys but then he came up to me and I copped one on the chin from him.

"I thought 'what the f---' so I flogged him".

In court on Friday, Brown pleaded guilty to charges of assault occasioning actual bodily harm and affray.

His lawyer said he came from a supportive family home and had good prospects of rehabilitation.

In seeking a non-custodial sentence, he also noted Brown was not the initial aggressor and was fuelled by alcohol.

However, in handing down the prison sentence, Magistrate Stoddart said a message needed to be sent to both Brown and to the wider community.

"The community is sick and tired of this type of behaviour," he said.