He was given an order to step back and failed to comply. Failure to comply according to our use of force rules using pepper spray is justified. The young man was between several parked police cars and the rioters in NYC have already set many on fire, jumped all over their cars, smashed out windows with bricks, and vandalised them with spray paint. The city should have a right to protect their equipment. You may disagree with this but if that order to move the crowd back came from a commander, the officer was going to obey it.