It may not be nearly so bad as other places, but when a police officer can detain, physically strike, and then arrest a citizen for not pulling up their pants... something is badly wrong. The Constitutional fig leaf here is presumably a law that requires people to wear their pants properly pulled up rather than low on the hips; ostensibly it regulates "gang signs" but in practice it appears to allow police to harass anyone they see violating the law. After all, there is a "violation" in plain sight which eliminates any need for probable cause of a more serious offense.
Once the initial contact is made the officer can respond to backtalk however he chooses... up to and including deciding to actually write out a ticket for the low-riding pants, and as soon as he decides to do that, he's justified searching anyone on the scene for "officer safety". Even if he doesn't find anything he's just spent 15-30 minutes harassing a citizen with threat of violence for not obeying a dress code. In the United States of America!
The cop in the video was fired. Which is comforting until you realize this is probably not the first time he's done something like this.