Maybe I missed something, but, I didn't see any heads bashed into the sidewalk, dogs shot, etc....(I skimmed through it). It looks like the the police had a reason to do what they did (*be there)... and let me tell you, if ever faced with the police, if you've done or didn't do anything wrong, you better just give in, and do exactly what they say... and it will be over that much quicker. They are there to 'sort out the arrests', and they are NOT there to determine guilt. That happens later... I remember a lady that actually called the cops on an abusive boyfriend... they arrested her because "She knew that she had her rights". Sure she did... but she showed it in an obstruction way. They arrested her on obstruction, and that is all, while they tried to sort everything out.
Call the cops, when they arrive, keep quiet, do exactly as they say, and don't be a loud mouth. Sure, the video's you see of injustice are out there, but it's up to you to help the idiot's do their job correctly.
*just be chill... Although, it's much better to be in a position that you don't have to deal with the police; not have jerk friends, the wrong part of town, etc. Just be chill and it'll be over before you know it.
////of course, there is the constitution, and you can use that, but ..... better to not be put into that position in the first place.