A teenager faces a life sentence after being found guilty of stabbing student Steven Grisales to death in a row over conkers.
The youth was found guilty at the Old Bailey of murdering the 21-year-old architecture student.
Mr Grisales died last August after he went over after a group of teenagers threw conkers still in their spiky shells.
He was walking to Silver Street station, Edmonton, north London, when he was attacked in College Close.
The youth, who cannot be identified for legal reasons, was remanded in custody to be sentenced next month.
After the verdict, Detective Inspector Richard Beadle said: "Steven did no more than stand up to unruly youths and for that he has lost his life.
"But for the courageous intervention of a local resident, I am convinced the attack would have continued.
"He placed himself in front of Steven whilst the youth continued to try to stab him.
"The defendant's arrogance and contempt for others belies his age."
Steven's mother Jasmid said in a statement: "Steven was always loved by every person who had the privilege of knowing him."
Andrew Edis, QC, prosecuting, told the trial: "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."
The accused blamed another youth for the stabbing, but was identified from his distinctive clothing on CCTV.
He claimed Mr Grisales had over-reacted and tried to hit him with a skateboard.Suggest a correction