edit: I just walked the video again. you have to be crazy if you don't think the guy was encroaching on the officer's space
There was a video where a bunch of riot police were riding on the outside of an SUV. One fell off of it to the ground, got back up turned around and pepper sprayed behind him, even though there was no one behind him. There was no one moving towards him or even near him.
I have said this elsewhere on HN, but I think these protests would be better for everyone if police simply did not show up. I think the video we are referencing is a great example why.