An Operation Wall Street protester was busted last night after he slugged a police officer during a march on the Federal Reserve.

About 100 demonstrators had left Zuccotti Park at around 10 p.m.

As the group neared Liberty and Nassau streets, two marchers began to fight each other.

When police tried to intervene, one of the protesters suddenly punched an officer in the face.

The man was taken into custody, but refused to identify himself.

He spent the night locked up as authorities struggled to figure out who he was.