There's the riot at NYU where more violent agitators showed up to prevent Gavin McInnes from speaking, where he was attacked with pepper spray.
On the night at Berkeley, a woman wearing a Trump hat was pepper sprayed while giving an interview for a news network.
These are the facts.
Call it what you want, but this is violence and destruction with the intent to silence people with an opposing point of view. It's not civil disobedience or protesting and more like terrorism.
As for your other question about whether or not I've heard of kettling, I have. The fact that it exists does not convince me that innocent bystanders need to fear that. In instances where you may have seen that, such as the inauguration of the president, charges were brought against some of those individuals. Which suggests the goal wasn't to arrest bystanders.
By the way, I don't know if you watched that one live or after it took place but there was a ton of chaos. People were throwing objects like glass bottles at the police in riot gear. Again, many of the people were dressed in all black with masks on. If you want a very real problem to attack, that's one to focus on.