Commissario
That's a taser. It's bright yellow. That video carries on and you can see a further puff from the right and he drops.Video I have just seen, shows the Police pulling off a member of the public (I guess), then you see what looks like a puff of smoke coming from where the armed copper is - end of video.
There's another video from another angle where you can see a lot of people around him, not just that single member of the public. Then they all scatter away, the member of the public is pulled off and you see an officer off to the right shooting him, single shot and he's dropped.
I wonder if the reason everyone scattered is because he pulled out a weapon. That would make sense and make him an immediate threat.