The teenager, who cannot be named for legal reasons, stabbed 16-year-old Luke Wallace during a confrontation in Glasgow in June last year.
Luke suffered massive blood loss from the wound which cut his femoral artery. He died in hospital eight days later.
His attacker was originally charged with murder but was convicted of the lesser charge of culpable homicide.
A jury at the High Court in Glasgow was told last month that the teenager admitted killing Luke, who played for Drumchapel Amateur Football Club, but claimed he acted in self-defence.
He said he had been attacked by Luke and another boy in Baillieston on 17 June last year.
He told the jury he struck out using a knife that Luke had dropped on the ground, after a lump of concrete and a piece of wood were thrown at him.
Defence QC Gordon Jackson said: “There was quite severe provocation. He was walking up the street with a girl and he was quite badly attacked. There was fairly severe violence shown towards him.
“This is someone who has been severely provoked and strikes one blow which results in terrible consequences.”
But the prosecution said the teenager had chased after Luke and had been carrying the knife before the attack.
Luke’s mother Angela Wallace, 49, told the High Court in Glasgow that just an hour before the stabbing she had texted her son asking where he was and telling him: “Be safe.”
She told the jury: “I know 100% Luke would never carry a knife.”
Sentencing the 17-year-old, judge Lord Woolman told him: “You stabbed Luke with a lock-back knife and he died several days later.
“You claimed he had brought the knife, dropped it and you picked it up, but the jury convicted you of having a knife in a public place.
“However, you were attacked first and only inflicted one stab wound.”
The Crown withdrew the murder charge and replaced it with the reduced charge of culpable homicide at the end of the prosecution evidence.
The teenager was also convicted of trying to defeat the ends of justice by washing blood-stained clothing he had worn on the night Luke, from Garrowhill, was stabbed.