No different from "Hello, 911, come quick there's a (insert MINORITY here) in my neighborhood and he's wearing those droopy pants and listening to music in a language I can't even understand!" When you grab somebody to make an arrest, some people take that personally, so you should have a damn good reason or else be prepared for a lawsuit. Even if he were a vagrant, they have to walk around somewhere and it might as well be around panicky people who call 911 for nothing.