Mixed martial arts fighter Rasul Mirzayev was found guilty of manslaughter on Tuesday but subsequently released, sparking fears that the court's decision could provoke nationalist riots.
Mirzayev stood accused of manslaughter over the August 2011 death of 19-year-old student Ivan Agafonov in Moscow.
He was sentenced to two years' imprisonment on Tuesday in the capital's Zamoskvoretsky District Court but released because a day in detention counts as two days in prison, according to Russian law.
Mirzayev, who has been detained since August 2011, has thus already served out his term.
News reports said police escalated security measures prior to Mirzayev's appearance in court, and there are fears that the release of the Dagestan native will ignite nationalist rioting. Several people who shouted political slogans outside the courthouse were detained Tuesday.
Dmitry Dyomushkin, a prominent nationalist and Russian March organizer, told Interfax that freeing Mirzayev would further aggravate nationalist tensions.
"Of course, such a development in the situation will not benefit interracial relations in the capital," Dyomushkin said. "We expect a deterioration, which will in one form or another spill onto the streets."
The victim's family left the courtroom early, and one relative was heard shouting that the death of a Russian on Russian soil would be punished, the Rapsi legal news agency reported.
Agafonov and Mirzayev got into a fight at a nightclub after Agafonov allegedly started flirting with Mirzayev's girlfriend. The martial arts champion punched Agafonov in the head, leading him to fall and hit his head on the pavement. The young man was hospitalized and died four days later.