Evren Anil died from a head injury eight days after the incident
Two teenagers who killed a man during a row over litter have each been sentenced to four years detention.
Evren Anil, 23, died from head injuries after he confronted the youths who threw litter in his sister's car window in Crystal Palace, south-east London.
Dejon Thompson, 16, of Thornton Heath, south-east London and Patrick Rowe, 17, from Tottenham, north London, admitted manslaughter at the Old Bailey.
Mr Anil's family described the sentence as "shocking".
Thompson and Rowe, who showed no emotion as they were sentenced, will be out in less than 18 months, having served half their terms minus the 210 days they have already spent in custody.
Judge Ann Goddard lifted restrictions banning the pair being identified and condemned their "yobbish and stupid behaviour".
She added: "The tragedy is that it need not have happened, if you hadn't started it or had had the courage to walk away."
Mr Anil's cousin Mehmet Aray said: "We expected five or six years to tell you the truth.
"We were prepared for that. But four years with good behaviour, out in two. In time for the World Cup I suppose.
"But you know, if that's the message that we want to send out to our kids then we should stop moaning about people being stabbed all the time."
Emigrated to Australia
Mr Anil had just started his first job after graduating with a first class honours degree in IT at the time of the attack last August.
He and his sister were waiting at traffic lights in her Peugeot 307 when Rowe threw a half-chewed Lion bar through the car's open window.
Mr Anil got out of the vehicle and threw it back at them, only for one of the boys to produce a 4ins knife from his trousers.
The knife was held to his throat and he was then punched in the face so hard that his skull was fractured, and he suffered a haemorrhage.
Mr Anil was born in Turkey and moved to London at the age of three with his family, settling in Upper Norwood, south east London.
Mr Anil's sister emigrated to Australia following the attack, and his mother and father have separated, said Mr Aray.