A row about youngsters throwing conkers led to the death of a 21-year-old student, the Old Bailey heard today.
Steven Grisales went over to talk to some youths who had been throwing the conkers still in their spiky husks.
But within minutes, Mr Grisales had been stabbed through the heart and died the next day.
A 15-year-old youth, who cannot be identified for legal reasons, denies murder.
Mr Grisales was walking to Silver Street station, Edmonton, north London, on August 31 last year, when he was attacked in College Close.
Andrew Edis, QC, prosecuting, said "This was a sudden, unnecessary killing as a response to a confrontation which took place in the street, which was about nothing very much.
"It was about throwing some conkers. Horse chestnut trees in north London shedding their conkers, people picking them up and throwing them about."
After Mr Grisales collapsed onto the pavement, local residents tried to help him. He was taken to hospital but died despite emergency surgery.
Mr Edis said two of the three youths handed themselves into police a few days later.
The accused youth handed in a prepared statement in which he put the blame for the stabbing on the third youth.
Referring to the incident which sparked the death, he said he and his friend were throwing conkers at two girls and the other youth.
He added: "We did so recklessly because one of the spiky objects went close to a man who was walking in the street.
"He was aggressive and abusive. he was very angry and the man crossed the road and picked up a skateboard and tried to hit me twice.
"I punched him in the face in self-defence. I saw my friend punch him in the chest."
The trial was adjourned until tomorrow.