A drug dealer stabbed a teenager to death as he was being held in a bear hug and was unable to dodge the blade.
Would-be DJ Connor Muir had punched Andrew Gibson in the face, smashing his nose, before an on-looker stepped in to try to calm things down and stop the fight.
Mr Muir then had no chance to ward off Gibson's knife and bled to death from a single wound.
The murder trial at the High Court in Edinburgh heard Gibson had also tried to hit Mr Muir on the head with a hammer.
A jury at the High Court in Edinburgh rejected Gibson's claim that he was acting in self defence but found him guilty of a lesser charge of culpable homicide.
The 23-year-old was remanded in custody for background reports and will be sentenced in December.
He was also convicted of two other knife attacks, assaulting another youth by punching and kicking him, dealing Temazepam and possessing cannabis, as well as carrying a weapon.
The trial heard how Gibson, described in court as a "violent bully",had received a phone call on March 6 challenging him to a fight.
He met 17-year-old Dario Fleming at a footpath near Rushbank in Ladywell, Livingston, for a square go.
Gibson had been armed with a hammer and a knife but the court heard no weapons were used in the brawl.
However, after fighting Mr Fleming, Gibson then turned his attention to a drug deal he was trying to conclude. His business was interrupted when Mr Muir of rushed up and punched him full in the face.
After the stabbing, kids who had been drinking vodka nearby were shouting and screaming for help and an ambulance was called to the scene. But medics were unable to save Mr Muir.
Prosecutors asked the jury not to believe Gibson's claim that he was acting in self-defence. Advocate depute Morag Jack said that by the time Gibson used his knife any danger had passed.
She said: "He carried out an act of extreme violence grossly disproportionate to being punched in the face."
The trial also heard allegations of an attempt to cover up after the stabbing by getting rid of the knife and washing Gibson's blood-soaked clothes.
However, both Gibson and his dad, 45-year-old David Gibson, were cleared when the jury found a charge of attempting to defeat the ends of justice not proven.
