Magistrate Robert Walker sentenced Jonah Bell, 19, to three months in prison after viewing CCTV footage of the assault, describing the attack as "disgusting".

He noted the attack was inflicted upon a school child, in front of other students.

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"This is a serious assault," Magistrate Walker said.

He said he was loath to send a young man to jail, but this case warranted such a sentence.

Documents tendered to court said Bell, who lives in Queanbeyan, said the school student was walking towards Bellambi train station with friends before he had a short verbal altercation with Bell and a 17-year-old woman on November 14.

The boy continued walking and began waiting for a train when Bell and the woman approached him, singling him out from his friends.

The woman said something to the boy before she alleged struck him in the head with her right fist.

Bell then came up to the boy, and "without hesitation", held him with his left and with his right clenched fist punched him about eight times in quick succession in the head and face.

The boy struggled to defend himself against the blows and he was knocked to the ground.

The boy regained his feet and Bell set upon him, punching him a further six to eight times in the head and face.

Bell and the woman left the area before the station manager took the boy into his office and contacted police.

The boy sustained swelling, lacerations and minor bleeding to his face and head. An ambulance was called and the boy was taken to Wollongong Hospital for further treatment.

"From the CCTV footage it is clear the victim was not behaving aggressively in any way towards [them]," the facts said.

"The victim does not attempt to retaliate against them."

Later that day, Bell was arrested and taken to Wollongong Police Station where he was charged with affray.

In court on Tuesday, Bell's defence lawyer Danny Lagopodis said the victim made a racist remark and "mumbled something that wasn't very pleasing" when Bell and a woman walked past.

He said Bell replied, "what did you say?" and the boy ran into the station.

Mr Lagopodis said Bell acknowledged it was "not proper" and he knew he should not have attacked the boy.

Mr Lagopodis asked Magistrate Walker to consider an intensive corrections order, but Mr Walker said Bell's behaviour needed to be denunciated.

Bell will be eligible for release in April.

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