Brett Buddle was set to face a week-long trial at Wollongong District Court, but changed his pleas to guilty on Monday after hours of negotiations.

His co-offenders, Sky Nikola Bozinov and Luke Paul 'Etch' Krajnovic, pleaded guilty to their role in the local court last year.

Buddle was drinking with two others on December 31, 2022, while next door on Adams Parade, Woonona, a backyard party was underway.

A firecracker from the party inadvertently landed in the backyard where Buddle was, agreed facts tendered to the court stated, upsetting the property owner's dogs. The neighbours apologised.

Later in the evening, Bozinov and Krajnovic arrived and exchanged New Year's greetings with a man, Kevin Gamble, who was vomiting in the neighbouring front yard.

Bozinov said: "Oi, you should probably make peace with the neighbour."

The situation escalated when the party host Shaun Petersen, intervened. Bozinov scuffled with Mr Petersen before Krajnovic, armed with a knife, stabbed him in the head and abdomen.

Krajnovic stabbed Mr Gamble as the fight continued despite the efforts of two other party-goers to break it up.

Documents state Buddle, armed with a piece of wood, stood nearby, and that one of the brawlers swung the wood at Mr Gamble, causing the wood to break before it was used to attack others.

More party guests intervened and broke up the fight. The trio fled the scene.

Mr Petersen, who was dragged to safety, was taken to St George Hospital with life-threatening injuries. He remained there for six weeks.

Mr Gamble needed surgery to his arm, including the insertion of a plate and 10 screws.

Buddle was arrested on January 4 and denied any involvement, telling police he left the brawl after hearing screaming.

He pleaded guilty on Monday to affray, assault occasioning grievous bodily harm, and three counts of assault occasioning actual bodily harm.

Bozinov was sentenced in September 2023 to 16-months jail, while Krajnovic will learn his fate in two weeks.

A date is yet to be set for Buddle's sentence.