The 25-year-old man was charged on Monday after he was arrested in Denmark in March. He has been detained since mid April.
During December's clash in southern Stockholm between neo-Nazis and Kärrtorp residents, the charged man was among those standing on the square when the Swedish Resistance Movement (SMR) showed up, reported the TT news agency.
He allegedly bludgeoned someone in the face.
Prosecutor Tove Kullberg explained that the process was dragging out because of the high number of suspects involved. Around 30 people were under investigation.
"There will likely be more charges filed," she said.
In April, an extreme-left activist was sentenced to six and a half years in prison for stabbing a neo-Nazi in the back during the same altercation.
Residents of the southern suburb had rallied to protest against the sprouting of Nazi graffiti when members of the Swedish Resistance Movement showed up. The scene quickly descended into violence with several people fighting back and several suffering knife wounds.
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The following weekend, Stockholmers gathered in their thousands to protest the violence.