FRINGE GROUPS UNEQUAL

The title of a story at Swedish news site The Local: Far-right extremists in violent clash with leftists. The clash described:

Far-right extremists clashed with a gang of left-wingers on the streets of Gothenburg early on Friday morning.

According to the police, the people involved are a group of far-right extremists and their left-wing opposites, the Afa (Anti-Fascist Action group).

So the opposite of far-right extremist is leftist.