Ricky Hayden, 27, was stabbed in Romford, east London, as he tried to stop his brother's scooter from being stolen on 13 September.
Tommy Roome, of Romford, was cleared of murder but guilty of manslaughter.
The 20-year-old was also cleared of the attempted murder and wounding with intent of Ricky's father Paul Hayden.
Tarrell Hinds, 20, of Chigwell, east London, was charged with the same offences and was acquitted on all counts.
The Old Bailey was told the minder, his father and brother Perry Hayden confronted the defendants, then aged 19, when Ricky was wounded several times in his leg.
Prosecutor Jonathan Rees QC said the defendants had gone to Gibbfield Close to look for two other brothers - Carter and Latham Jordan - with whom Roome was involved in an ongoing dispute.
He added: "It appears that confrontation came about because the Haydens believed that Tommy Roome and Tarrell Hinds had designs on Perry Hayden's moped which was parked directly outside the front door of the Haydens' home address."
Giving evidence, Roome said they had stopped as they thought they saw one of the Jordans' cars when he spotted three men running down the road.
He told jurors he only put his hand on the handle of his knife when he saw Paul Hayden had a baseball bat.
Roome said he was not aware he had hit Paul Hayden and insisted he never intended to try to kill him or do him really serious harm.
"There was just blood in the road. I panicked and ran down the road," he added.
Ricky Hayden acted as a bodyguard for celebrities including footballer Peter Crouch and model Abbey Clancy.
Sentencing will take place at a later date.
A man has been found guilty of killing a celebrity bodyguard who confronted machete-wielding youths outside his home.