Kent thug Paul Ojo has been sentenced to 16 months after group attack of teenager during April this year.
Ojo, 19, punched the victim twice in Upbury Way in Chatham.
The attack was caught on CCTV and Ojo was later identified by the Metropolitan Police.
He was arrested, charged with causing actual bodily harm and admitted the crime when he appeared at Maidstone Crown Court, last week.
DC Mark Donovan, who investigated the incident, said: “This was an unprovoked and cowardly attack on an innocent young man.
“The victim was walking through Chatham, when a group of men, including Ojo, began shouting at him.
“While the victim was trying to calm the situation, Ojo, bolstered by the presence of his friends, assaulted him from behind.
“No person should suffer this treatment and I hope Ojo reflects on his actions and improves his behaviour while behind bars.”