A jury deliberated a few hours before finding Mahad Ahmed guilty in the death of 25-year-old Michael Louis Beaver.
Ahmed, 24, faces at least 15 years to life in prison when he is sentenced June 12.
Deputy District Attorney Melissa Vasel told jurors that Beaver, his brother and a male friend were wrapping up a night of drinking and partying about 1 a.m. last June 15 when they encountered the defendant's group -- which included four men and one woman -- outside the Encore club on F Street.
The victim's brother fell ill and started throwing up, causing the woman in Ahmed's group to say, "That's (expletive) nasty!", according to the prosecutor.
When Beaver reacted to her comment, the woman slapped him, and then a man in the defendant's group hit Beaver in the mouth, according to the prosecutor.
After Beaver and the man who hit him squared off, Ahmed decided "to launch his fist into the victim's skull," knocking Beaver back and causing him to hit his head on a metal railing, Vasel told the jury.
"None of it was warranted. This wasn't a bar fight," the prosecutor said in her closing argument.
A witness at a nearby bachelorette party told police she saw the defendant run up and "blindside" the victim, who died at a hospital about an hour later.
Police learned that Ahmed had been arrested later that morning following a disturbance at a City Heights hookah lounge, and he was re-booked on a murder charge, Vasel said.
The victim's blood was found on several spots on the shirt that Ahmed was wearing the night Beaver died, according to the prosecutor.
She said the victim died from a catastrophic arterial injury, or bleeding on the brain, telling the jury that he never got back up after being punched by the defendant.
Defense attorney Kathleen Lee said Beaver was intoxicated and kept coming forward after being punched in the mouth by a man in the defendant's group. She said Ahmed then stepped forward, punched the victim, and the entire group walked off in an altercation that lasted all of six seconds.
Lee said Beaver died from a "unique injury" and that his death was "unintentional."