At least one demonstrator was arrested as punches flew at far-right hatemonger Jake Lang’s “Crusader March” outside City Hall during 9/11 memorial ceremonies Friday, sources said.

Nearly 200 protesters with Lang’s clownish anti-Muslim march and counterprotesters clashed near Church Street and Cortlandt Way in Lower Manhattan, the sources said.

Whether one of Lang’s allies or a counterprotester was arrested wasn’t immediately clear.

Lang’s march drew a small crowd, who brandished signs declaring “Deport All Muslims” and broadly blaming Islam for the Sept. 11, 2001 terror attacks.

The ugly scene drew antiracist counterprotesters — as well as a group of apparent neo-Nazis wearing swastika armbands.