A Czech court acquitted the frontman of US heavy metal band Lamb of God of manslaughter charges in the death of a fan who was pushed off the stage at a concert in Prague.

The prosecution accused Randy Blythe (42) of shoving 19-year-old fan Daniel Nosek off the stage at the 2010 concert, causing him to hit his head when he crashed onto the floor.

Mr Nosek died in hospital a few weeks later from his head injury.

Presiding judge Tomas Kubec ruled that Blythe's actions did not constitute the crime of causing an injury leading to death.

"We did not find criminal responsibility in the actions of the defendant. We found moral responsibility. There has been the death of a young man who had not been guilty of anything."

Mr Kubec said the concert promoters were ultimately to blame for failing to prevent fans from clambering onto the stage. "We reached the conclusion that there was a serious fault on the side of the promoter and organiser of the concert."

Prosecutors immediately appealed against the acquittal, meaning that the case will be reviewed by the Czech High Court.

Blythe, who has cropped his long dark hair but kept his soul patch, wore a dark suit with white shirt and a striped tie at the trial, attended by Czech and international media.

"I have been found not guilty and acquitted of all charges against me. I am a free man," Blythe said in a post on his Instagram.com profile.

"Please remember the family of Daniel Nosek in your thoughts and prayers in this difficult time. I only wish for them peace. Thank you for your support."

Blythe nodded his head when the judge said some form of compensation for the victim's family could be suitable.

"The acquittal does not prevent the defendant, if he feels some moral responsibility, to enter negotiations with the family of the victim and act accordingly," the judge said.

The singer admitted to shoving the fan off the stage after several other fans climbed up onto it during the 2010 Prague show, but said he believed Mr Nosek was unharmed.

He said he did not learn of Mr Nosek's death or the prosecution over the incident until police arrested him at Prague airport when the band returned for another gig in June last year.

Blythe made no immediate comment to reporters after the ruling and left with his attorney.

He was released on bail after his arrest and travelled back to the United States, but returned for his trial. Blythe would have faced up to 10 years in prison if convicted.