[nimble]

The proxy angle is interesting, but I don't think that's main factor here. What's walking through someone's lawn a proxy for? The cops see a kid who looks like trouble and who's technically breaking the law and they arrest him, whether the specific crime is a proxy for anything or not.

And then there's the question of what "the spirit of the law" means. The courts wouldn't allow a blanket prohibition on "gang activity," even if that may be what legislature had in mind.