From my own experiences having seen incidents like in the video from here in Ireland,the UK,Northern Ireland and across the world I would have to say that a sizable number cops no matter what the police force seem to take great delight in assaulting the common citizenry of their countries when they are in a confrontational position.I'm guessing that those cops who do this just are power crazy and get theior kicks from being given free reign to administer what they see as justice,Theres been similar scenes here in the recent past,a peaceful protest on Mayday 3 or4 years ago saw cops administering beatings to whomever was within range of their batons.They have done the same to protesters peacefully demonstrating against an Oil Company building a pipeline in their area over safety concerns.
Now I've also had dealings with cops and been in troublle with them once but have found those cops to be even and fair in their execution of their duty,but at rthe same time have found others to be arrogant rude and downright nasty in their attitudes.
I also think that some cops take great pleasure in releasing their anger at certain sections of society in such confrontations as the one in the video.