Three men were facing life sentences today for killing an IT expert after snatching his girlfriend's Halloween hat.
Ben Gardner, 30, was punched to the ground where he lay helpless as one of the men kicked his head "as if taking a penalty".
Allanna Devine, 28, was also punched in the attack on October 31 last year, the Old Bailey heard.
Daniel Ransom, 21, Ross Collender, 21, and Jordan Dixon, 18, all of Carshalton, Surrey, were found guilty of murder by 11 to 1 majorities.
Sarah Davey, 41, of Sutton, Surrey, was found not guilty of assisting an offender by harbouring Dixon.
Mr Gardner, who worked for insurance firm Legal & General, had been to a club with Miss Devine to celebrate her birthday and Halloween.
She was dressed in a pirate's outfit, with a black wig and hat. He had a black leather jacket and vampire fangs.
In the early hours of the morning, Miss Devine was waiting for Mr Gardner outside a kebab shop in Sutton when a group of men snatched her black hat and wig.
Miss Devine broke down as she spoke of Mr Gardner's last moments.
She said: "My hat and my wig were taken from my head. I was not concerned about it because it was the end of the evening, but I did say 'Can I have my hat back, please?'
"I was greeted by jeering. They were very loud."
After getting near her flat round the corner, she told Mr Gardner what happened.
She said: "Ben decided he was not happy that my wig and hat had been stolen and he was going to approach the group about it."
As he went off, the verbal abuse increased and she heard herself being called "a big fat moose", before she saw her boyfriend returning with her wig.
Miss Devine said she decided to approach a youth who was calling her names and asked him: "What is your problem?"
She continued: "I was hit in the face by him. I was fuming. I said 'You are a big man to hit a woman'."
She told the court she was aware of Mr Gardner behind her and the group "flared up".
She remembered one of the men jumping up and down and taking his jacket off.
Mr Gardner said: "I am not a fighter but I have just seen someone hit my girlfriend and I am not standing back and letting you hit my girlfriend."
Miss Devine said she could not remember the rest of the attack except hearing a friend scream.
"I ran back round to see Ben..."
Brian Altman QC, prosecuting, has told the court that CCTV footage showed the incident unfold.
He said: "As Miss Devine went to pick up a black witch's hat which had been thrown by someone unconnected into the road, Dixon booted it away.
"Ransom kicked and stamped on it and, in a quite provocative and contemptuous act, spat in it and threw it at her."
Then Collender "suddenly and unexpectedly" punched Mr Gardner on the left side of the face, said Mr Altman.
As he recoiled from the blow, Mr Gardner was punched by Dixon and fell on to his back in the road.
Mr Altman said Ransom then kicked an "utterly defenceless" Mr Gardner.
"This was a completely unjustified attack, an escalation of violence," he added.
"Ben Gardner never stood a chance. He never laid a single finger on anyone.
"The reaction of Ransom and Collender was to run - big cheesy grins on their faces."
Witness Sean James said: "I saw a punch being hurled. He stumbled. He got hit again. Then he hit the ground and he was lying in the road.
"Then another man kicked him in the head. It was very ferocious - as if he was kicking a football.
"While he was on the floor, another man - I think it was someone who previously punched him - did an arm movement and said 'It's over, you are out'."
Mr Gardner died in the early hours of November 1 last year from "catastrophic brain damage".
The three were remanded in custody to be sentenced on Friday. Judge Richard Hone said they would be jailed for life but he had to fix a minimum term.
Miss Devine wept uncontrollably at the back of the court as a statement by Mr Gardner's father, David, was heard.
It said: "I cannot forgive these people for what they have done, they have destroyed me and my family for the rest of our lives."