The defendant, who was just 15 at the time of the attack and cannot be named for legal reasons, had denied the manslaughter of Arkadiusz Jozwik, but was found guilty after a trial at Chelmsford Crown Court.
Mr Jozwik, 40, had been drinking vodka with two friends and had just bought a pizza when he was set upon outside a row of takeaway shops in Harlow, Essex, shortly after 11.30pm on August 27 2016.
He died two days later in hospital from head injuries.
Rosina Cottage QC, prosecuting, had told the trial that the defendant hit Mr Jozwik with a “Superman punch” in the back of the head.
She added: “He had no intention to cause really serious harm to the deceased. However, by using the force he did, taking a man completely by surprise from behind, he must have been aware that some harm was likely.”
Mr Jozwik and one of the friends he was with were “significantly affected by alcohol and their behaviour was affected by it” while they were in The Stow shopping precinct, Ms Cottage said, adding that they had approached the youths.
The court heard the defendant had two previous convictions, one for possessing half a knuckle duster and the other for threatening behaviour, and was on bail for a separate matter at the time of the attack.
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Patrick Upward QC, mitigating, said Mr Jozwik’s injuries were caused by him hitting the ground and not from the punch itself.
“The deceased and his companion, according to the witnesses called by the prosecution, were staggering from drink,” said Mr Upward. “They made racist remarks to the youngsters, then invited violence from them, and they were considerably bigger and stronger than the young people.
“It was after the deceased pushed one of the youngsters that this defendant did what he did and that presents a different picture from the hullaballoo that arose after this incident took place.”
He described the defendant as a “shrimp” who was “5ft something and weighs less than 10 stone”.
He said the teenager had a troubled family background, his father has cancer and a psychologist’s report found the defendant was remorseful.
“He said he wanted Mr Jozwik’s family to know he did not intend to hurt him and takes responsibility for what he’s done and is extremely sorry,” said Mr Upward.
Judge Patricia Lynch said Mr Jozwik was a “perfectly decent, upstanding, well-loved man in his prime” and described his death as “tragic”.
She said no sentence she could pass would “make up for the massive loss that (Mr Jozwik’s family) have suffered and will live with for the rest of their lives”.
She told the defendant: “I’m dealing with a case where you approached Mr Jozwik from behind, taking him by surprise and hitting him once to the head.
She said that Mr Jozwik suffered “catastrophic head injuries from which he never recovered, adding “thereafter you fled the scene”.
The court heard that Mr Jozwik’s family took “some comfort” from the guilty verdict.