Richard Everitt provided an easy target for a gang of Asian youths out for vengeance on another white youth, John Bevan, prosecuting, told the Old Bailey.
The 10-strong gang had gone to Somers Town, north London, hunting for a youth called Liam they suspected had stolen jewellery from a fellow Asian.
"It is plain the group's blood was up - their purpose was to punish Liam or anyone else convenient," said Mr Bevan.
He said Richard had been on his way home with two young friends, carrying some pot noodles he bought after playing football on a local green.
One of his alleged killers was later seen eating noodles while talking of the attack, according to the prosecution.
Mr Bevan said that as Richard and his football companions walked back from King's Cross, the Asian gang surrounded them. One of Richard's friends was asked if he knew Liam and was headbutted and punched when he replied "No".
The friends ran but Richard was not as fast as the others and was an easy target for the pursuing gang and was stabbed between the shoulder blades as he ran. He staggered before collapsing on the pavement and died shortly after from the single wound which penetrated his ribs, right lung and heart to a depth of seven inches.
Abdul Hai and Badrul Miah, both 20, deny murdering Richard in August last year. They, along with 19-year-old Showkat Akbar, also deny conspiracy to inflict grievous bodily harm on Liam, whose full name has not been given, and violent disorder.
Hai and Miah deny perverting the course of justice by trying to get a teenage girl to provide false alibis for the murder.
Mr Bevan said: "No one, apart from the Asians involved, knows what happened as no one actually witnessed the killing." There was no evidence Richard had been fighting, so "he must have been the victim of ... a brutal attack from behind". He said he was not saying either of the defendants was the knifeman but that the attack was a joint enterprise. He alleged Miah was the ringleader and Hai was with him. About 20 minutes after the stabbing, Miah and Hai joined a group who were talking in the street. Miah was eating a pot noodle and Mr Bevan said: "He told the group they had 'stabbed up a white boy'."
Mr Bevan said blood matching Richard's had been found on Miah's jeans so he must have been close to the attack.
The trial was adjourned until Monday.