Shaun Garry Johnson on trial for alleged stabbing murder of Steven O’Brien

The defence has suggested a Newcastle man was defending himself when he fatally slashed his mate’s throat during a Boxing Day family gathering.

A key witness in the case against a Newcastle man who slashed his mate’s throat at a Boxing Day party has admitted he was asked to bash the knife-wielding attacker.

Shaun Johnson, 38, is standing trial in the NSW Supreme Court having pleaded not guilty to the murder of Steven O’Brien, 50.

Johnson has pleaded guilty to the lesser charge of manslaughter, claiming he acted in self defence.

Steven O'Brien with four of his seven children. Picture: Supplied.

Billy Gee, who was drinking with the two men at Mr O’Brien’s Mayfield home late on December 26, 2019, previously told the judge-alone trial Johnson lashed out after accusing the victim of sleeping with his partner.

But on Friday defence barrister Chris Watson suggested Mr Gee was asked by a friend during an earlier jail stint to assault Johnson.

“Nope,” Mr Gee responded.

Asked a second time he said of an associate, “he did say something along those lines when I was in jail but I took no notice of it”.

He also denied striking Johnson, causing the accused to act in self defence, or that Mr O’Brien was armed with a shovel.

Steven O’Brien died after his jugular vein was severed. Picture: Facebook.

“I didn't touch Mr Johnson one thing, not at all,” Mr Gee said.

“One hundred per cent I disagree, I didn’t touch him … I don’t hit people mate, I’m not a fighter.”

Mr Gee maintained Johnson slashed Mr O’Brien’s throat in an argument over cheating allegations.

He also denied telling responding police Johnson reacted because he was “trying to bash him or some s**t like that”.

Visibly agitated, Mr Gee told Mr Watson he was doing a “pretty s**t job” of questioning him before requesting a break from court.

The trial before Justice Richard Cavanagh continues.