Shaquan Fearon, 17, from Lewisham, south east London, was stabbed on 3 September last year as he walked along Turnham Road in Brockley with a friend.
Two boys, aged 15 and 16, are on trial at the Old Bailey accused of his murder and the attempted murder of Junior Inneh, who was wounded in the attack.
Both defendants, who cannot be named for legal reasons, deny the charges.
Prosecutor Brian O'Neill told the jury that Junior, 18, sustained a "wound to his face and cuts to his clothing".
He said: "Much of the incident was captured on CCTV and witnessed by local residents."
Mr O'Neill said the events leading up to the stabbing had been pieced together, although the motive was not clear.
The court heard that  Junior and Shaquan were walking towards a youth club when they were approached by the defendants.
The 16-year-old asked Shaquan where he was going and was told it was "none of his business". The 15-year-old then grabbed Shaquan's body warmer and was hit in the face by the victim, jurors were told.
Two knives were produced by the older defendant and one was passed to his co-accused, the court heard.
The victims, who were not armed, ran away but were chased by the defendants who attacked Shaquan together, Mr O'Neill said.
The case continues.
A teenage boy was killed in a "murderous knife attack" in the street by two younger boys, a court has heard.