"I had forgotten that there could ever be domestic conflicts where law enforcement were not themselves belligerents." ouch. Must be weird living where you live.
Conflicting football ultras is basically the only case where this doesn't happen.
(I've never been near a tear gas kind of event, but I did witness the Met Police deploy "kettling" for the first time in May 2001, close enough that if I'd not paid attention to the police lines forming up I would have been imprisoned uncomfortably for eight hours.)