It really looks like the cops orders were "use any excuse to attack the white germans".

The blue jacket guys look like they had the knife guy half restrained when the cop rolled in and knocked attacked him knocking him off of knife guy.

The only guy acting rationally was the foreign guy cop, because he wasn't playing "good race bad race" he was playing "guy with a knife, guy without a knife".

I think blue jacket guy was somewhat restraining stabby guy, when the cop tackled him freeing stabby guy.

The camera is pointing just slightly away so you catch a few moments of it.

In any other circumstances you'd assume the cop just mosread the situation, bit I feel like here the cops orders were to use any excuse to attack the people the current politicians don't like, so he followed through on that thinking it was a fist fight so he could not care that he's going after the wrong person.

It looks like blue jacket guy was restraining in some way stabby guy, then the cop tackled blue jacket guy off of him freeing up stabby guy. Freed by the cop, stabby guy then stabs the cop from behind.