Nick Baty went into a coma and died a month after the attack.
A teenager has been found guilty of killing a 47-year-old man who tried to give medical help to a young friend.
Nick Baty was stamped on and kicked by Joseph Thomas, 18, outside a gym in Brackla, Bridgend, south Wales.
The passer-by had gone to the aid of a boy who had collapsed after drinking. Mr Baty died a month after the attack after slipping into a coma.
Thomas denied murder but was convicted of manslaughter at Cardiff Crown Court and will be sentenced on 15 December.
Father-of-one Mr Baty was returning from a funeral when he stopped to help the boy outside the Physique gym on 4 January this year.
The court heard how Thomas, who was 17 at the time of the attack, had previously been drinking with the boy and threw Mr Baty to the ground and repeatedly stamped on his head.
Prosecutor Roger Thomas QC said: "This was a vicious attack carried out by Thomas.
"Mr Baty was only concerned about the welfare of the teenager unconscious on the floor.
"Mr Baty moved towards the unconscious teenager when, suddenly and without warning, Thomas ran at him from behind shouting 'Leave him alone'.
"He grabbed him by the shoulder and threw him to ground.
"Mr Baty's head struck the ground with a thud but Thomas didn't leave him - he attacked him as he lay defenceless on the ground."
The court heard Thomas left Mr Baty lying in a pool of blood and bragged to a friend about what he had done.
His friend called 999 and police found Mr Baty lying next to the unconscious friend.
Mr Baty was put on a life support machine but never recovered and died in hospital from a head injury, pneumonia and a blood clot.