Stinging gas sends May Day protesters fleeing - Article Photos 5/16

Violence erupts during a May Day march and protest in Portland, Ore., Tuesday, May 1, 2012. Up to 100 protesters set out on an unpermitted march late Tuesday morning. Some got off the sidewalk and into the street. Police on horses and bikes tried to push them back onto the sidewalk, and a shoving match ensued. (AP Photo/Don Ryan)