Yes, I watched the video. From a police standpoint the amount of force is relatively low. Again, the likely legal justification for the action is that protest made identification impossible which allows them to separate the person from the protest to id him. Him falling was not intended. Injuries caused by resisting are legally speaking no harm done by police. They did not hit him; they could be allowed to if he resisted.

Anyway, I am trying to explain the legal side, but I am no lawyer. Just interested in law. You can try r/polizei to get a more "official" answer. I don't think there's a community for German police on reddit yet.

Imho: I would have let the man be as long as he doesn't get closer. It looks like he's carrying a beer and the trouble is not worth it for "pig". Police usually has room for not engaging if it helps keep protests civil. I think, this didn't go well - especially because the officer tried it alone at first.