The 21-year-old, from Alexandria, has pleaded not guilty to charges of recklessly causing grievous bodily harm, and affray.

During the third day of a hearing in Wollongong Local Court, Sa testified that his single punch, which severely fractured Cameron Shaw's skull and left him with bleeding on the brain, was thrown in self defence.

Mr Shaw and seven friends were on a bucks weekend on February 9 and had been drinking at the Glasshouse Tavern before the fight broke out around 3.30am, the court heard earlier this week.

Sa's punch followed a scuffle between Mr Shaw's friend, Andrew Dickson, and Roosters player Shaun Kenny-Dowall outside Oporto's chicken shop, witnesses told the court.

Mr Kenny-Dowall had accused Mr Dickson of stealing money from his wallet. A verbal argument ensued, which then spilled out onto Crown St and eventually became physical. "I was scared, I wanted to get out of there," Sa said.

"(But) I was more scared about my friend (Kenny-Dowall) being hurt ... I thought he was going to get kicked in by 10 or 12 guys."

Sa, who said he had consumed at least two schooners and up to eight vodka drinks that night, denied being affected by alcohol. He said he was trying to coax Mr Kenny-Dowall to leave when he began to feel threatened by Mr Shaw's group of friends.

When asked by police prosecutor Sergeant Shannon Ryan if Mr Kenny-Dowall's aggressive behaviour "was the problem", Sa replied "Yep".

After feeling a slight push to his back, Sa "just reacted and threw a punch", he told the court.

He denied celebrating the punch by shouting "Woo" and laughing.

Sa also denied that Mr Kenny-Dowall phoned him and asked him to join the fight.

Sa's evidence was supported by team-mate Jarvan White, who also gave evidence yesterday.

The hearing, before Magistrate Paul Johnson, was adjourned until Wednesday, December 17.