Video of the confrontation in Bay Ridge on Saturday shows a person throwing a helmet into a crowd of people gathered for a 'Blue Lives Matter' rally.
The helmet struck a police officer in the head. He was treated for minor injuries.
Police arrested Robert Bolden for the assault after officers used a taser to subdue the suspect.
Bolden is being treated at a local hospital. Charges are pending.
RELATED: Video shows man attacking NYPD officer trying to break up fight