A CHAMPION boxer has admitted carrying out a brutal attack on a teenager - but claims he only acted in self defence.

Grant Quigley, 17, confessed to the High Court in Glasgow that he had left the 19-year-old victim lying unconscious in Port Glasgow's Brown Street after punching, kicking and repeatedly stamping on his head.

But taking to the witness box yesterday, he denied attempting to murder the man, insisting he had only fought back to protect himself, fearing he was about to be stabbed.

Quigley said: "I was scared, he told me he had a knife.

"I never tried to kill him. The adrenalin was pumping and I just lost it. I never believed his life could be in danger."

During a dramatic fourth day of the trial, the Crown dropped the attempted murder charge against one of Quigley's co-accused, 18-year-old Lee Doherty.

Doherty had a plea accepted to a lesser charge of assaulting a female and seizing a mobile phone from her - but was brought back into the court just moments after walking from the dock to give evidence on Quigley's behalf.

Quigley also told of his promising boxing career that now lies in tatters.

He told how he had successfully represented Scotland at the Commonwealth Youth Games last year and won a host of national and British amateur titles, adding: "I hoped to have a career in boxing. Representing Great Britain should have been next for me."

Quigley claimed that he had been bullied through school by the complainer, adding: "I was picked on for over two years. It got so bad I had to be escorted from class to class by the depute head and had to stop getting the school bus."

The trainee scaffolder told how he had been drinking with Doherty and fellow co-accused Michael Murray, 18, on the night in question when they were approached by the man and his friend at a roundabout near Tesco.

He told how he had tried to walk away from a confrontation before claiming the victim then threatened to stab him.

Quigley added: "He ran at me and reached round his back. I thought he had a knife and we began fighting.

"He said he was going to stab my eye, that he was going to batter me like he had my brother."

The 17-year-old was played CCTV footage of the brawl, which showed him repeatedly kick, punch and stamp on the victim as he lay motionless on the ground.

When asked by QC Joe Barr, appearing on behalf of principal solicitor Gerry Keenan, if he regretted his actions, Quigley looked at the ground and said: "I am totally disgusted and ashamed of myself. I wish I had never done it. I regret it every day."

Mr Barr added: "You accept your guilt, don't you?"

Quigley replied: "Yes. Yes I do."

Both Quigley and Murray had already offered to plead guilty to assaulting the man under deletion of attempting to murder him, endangering his life and leaving him permanently impaired, but had their offers rejected by the Crown.

Advocate depute Lesley Shand, prosecuting, suggested to Quigley that he had launched his assault with intent to seriously harm his victim.

She said: "You stood there, the champion boxer with his two friends, and didn't run away. You hated this man and you wanted to do serious harm.

"You were the aggressor and you went after him to inflict damage."

Quigley replied: "No."

Doherty was then dramatically brought back into the dock as a witness, an option that only became open to Quigley's defence team when his co-accused's plea was accepted yesterday by the Crown.

Doherty claimed that he had looked on as his friend was intimidated by the complainer before the pair began to fight.

He added: "I thought the man had a knife. He was right in Grant's face and then he tried to punch him."

When asked about the CCTV that showed him trying to drag Quigley away from the man as he lay on the ground, Doherty added: "I struggled to stop him. He is fitter and stronger than me. I don't even know if he knew I was there."

Murray's defence counsel declined the opportunity to put him in the witness box.

Quigley, of Hillside Drive, and Michael Murray, of Benview Road, both Port Glasgow, are charged with attempting to murder the 19-year-old on 20 November 2010.

They are charged with repeatedly punching and kicking him on the head and body, causing him to fall to the ground.

Both are further accused of repeatedly punching and kicking him for a second time before repeatedly jumping and stamping on his head and body, all to his severe injury and to the danger of the man's life.

Doherty, of St Mary's Wynd, Stirling, was ordered to return to court to be sentenced at the conclusion of the trial.