Karl James Greenland, 18, is accused of jumping on the 19-year-old victim's head with such force a loud cracking noise was heard by witnesses to the assault, described yesterday as "sickening."

On Saturday night, the alleged victim, from Horsley, and a 20-year-old friend attended a party in Corrimal, but the event was shut down after a fight broke out between the pair and another group of males, facts before the court said.

The victim and his friend walked to Corrimal Railway Station but while standing on the platform were allegedly set upon by Greenland and a group of up to 10 males.

During the assault the victim was kicked in the head by one of the group, causing him to fall unconscious to the ground, the court heard.

According to the tendered facts, Greenland stood over the motionless victim, punching him in the face.

Greenland was dragged away and four other males continued kicking the Horsley teen in the head which jolted backwards with each impact, the facts said.

Police will allege Greenland then jumped on the unconscious victim with such force a loud cracking noise was heard.

An hysterical bystander began yelling, "He's dead, he's dead," before the group fled, the facts said.

The victim suffered a broken jaw which was surgically re-attached with a plate.

Police prosecutor Sergeant Darryl Hahn described the facts as "sickening," and said the assault was a "vicious, savage attack" involving an extreme level of violence.

He said there were a number of witnesses and also video evidence of the attack.

Sgt Hahn told the court police later seized a mobile phone from Greenland and allegedly found messages bragging about the attack.

One read: "That was me haha ... some c... hit me with his sk8 board lol, then I dropped him, it's in the paper lad, all of it was at the traino."

Opposing bail, Sgt Hahn said community safety was paramount.

Legal Aid solicitor Tyrone Phillips, acting for Greenland, said the fight originated from allegations involving the victim and a young woman. He said the fracas had broken out after his client was hit with a skateboard and that Greenland denied stomping on the teenager's head.

In applying for bail, Mr Phillips said Greenland could report daily to police, live with his father and post a surety.

Magistrate Ian Guy yesterday refused bail and adjourned the matter to August 29 when Greenland will appear via videolink to face charges of affray and causing grievous bodily harm with intent.

A 17-year-old boy also charged in relation to the attack appeared yesterday in Campbelltown Children's Court.

He will appear in Port Kembla Children's Court on July 23.