A motorcycle gang leader accused of killing a high-ranking Hells Angel rival said he shot him at a Las Vegas casino in self-defence.

Vagos leader Ernesto Gonzalez, 55, is accused of shooting Angels boss Jeffrey "Jethro" Pettigrew in 2011 after a fight broke out at a Sparks casino in Nevada.

Gonzalez, president of the Vagos chapter in Nicaragua, pleaded not guilty to murder and conspiracy to commit murder in what prosecutors claimed was part of an organised assassination plan.

Gonzalez's lawyer, David Houston, said he fired at Pettigrew because he feared he was kicking another Vagos gang member to death.

"Ernesto Gonzalez was put in a position of making a decision: Do I do nothing and let that happen? Or do I fire this weapon," he said.

Houston said that CCTV footage of the incident would show Gonzalez attempted to move away from the trouble that had been started by another Vagos member.

A court heard that after the shooting began, people inside the Sparks casino carried on gambling regardless.

"Some of them were still playing slot machines," former casino security director George Messina said. "Some of them were trying to get their money out of slot machines. Some of them were hiding."

Another Vagos member, who police blamed for starting the fight, pleaded guilty in March to murder.

Gary "Jabbers" Rudnick, former head of the Vagos Los Angeles chapter, will be sentenced in August. Police said he repeatedly taunted Pettigrew until he was punched, which led to the shooting.

Elsewhere, Hells Angel Cesar Villagrana pleaded guilty at Washoe District Court to one battery with a deadly weapon. He faces up to 15 years in prison.