Testimony over a brawl at the Metropolitan Republican Club has focused on extremists who also skirmish online.

By Colin Moynihan @ NYTimes.com, Aug. 8

A New York City police detective, when asked on the witness stand this week how he had identified members of a far-right group called the Proud Boys, gave an unexpected answer: the department, investigating a brawl in the city last October that involved the group, had relied in part on information posted online, much of it gathered by anonymous, self-described anti-fascists.

“There was a tremendous amount of what we call ‘doxxing,’” the detective, Thomas Mays, testified, using a slang term for the practice of disclosing personal information online. “Names that were given for the individuals.”

For the past week, jurors in State Supreme Court in Manhattan have been immersed in the unfamiliar world of the Proud Boys and their political enemies, often known collectively as Antifa. They have heard testimony about a subculture of battling groups, described as extremists who fight not only in the streets but also online.

The trial concerns the events of Oct. 12, when Gavin McInnes, the founder of the Proud Boys, appeared at the Metropolitan Republican Club on East 82nd Street [....] Protesters had gathered outside.  Afterward, as multiple videos show, 10 members and associates of the Proud Boys surrounded and beat four people — believed by the police to have been members of Antifa —who had circled the block to approach them. The four who were assaulted refused to talk with the police. They were identified in an indictment only as Shaved Head, Ponytail, Khaki and Spiky Belt. Their whereabouts are unknown.

With no victims to put on the stand, prosecutors have relied on video to make their case [....]