Marcus Ramsay was an innocent bystander who had been trying to defuse violence when the 35-year-old was fatally wounded after violence erupted at a street party in Firth Park last August.
Ruben Moreno, 18, formerly of Aldfield Way, Longley, was found guilty of murder, following a five-week trial at Sheffield Crown Court which concluded in June.
His friend Isaac Ramsey, also 18, and formerly of Andover Street, Burngreave, was found guilty of manslaughter.
Mr Ramsay was killed when an altercation at the street party on Horninglow Road escalated into significant disorder.
Moreno and Ramsey, then both 17, had attended the party while armed with knives.
At the party, in the early hours of Saturday, August 8, a 24-year-old man was slashed across the chest and abdomen, triggering a chain of events which led to Mr Ramsay being stabbed to death by Moreno 17 minutes later.
Jurors heard that Mr Ramsay had been trying to prevent Moreno and Ramsey from chasing his brother through the crowds when the fatal wound was inflicted.
Three other men were also stabbed that evening, all in unconnected incidents.
After Monero and Ramsey were found guilty of their parts in Mr Ramsay’s death DCI Mark Oughton, the senior investigating officer, said: “This case yet again lays bare the horrors brought by knife crime.
“Marcus Ramsay was an innocent bystander, whose gut instinct was to intervene and protect his brother from two teenagers he could clearly see were armed. Marcus was doing his very best to defuse a dangerous situation. He wasn’t involved in the evening’s violence; he was trying to put a stop to it.”
Monero and Ramsey, who went on the run for weeks after the killing, are to be sentenced today.
DCI Mark Oughton said: “Both friends had a propensity for carrying weapons. The streets of South Yorkshire will be safer without them.”
The statutory sentence for murder is life.
Judges then set the minimum number of years killers have to spend behind bars.