It's a really bad idea to be protesting in the middle of a street and block a cop car, then jump on top of the cop car and think the officers are going to just sit there. Nope, they're going to drive away and if you're still on top of the cop car at that point, then that's your own fault for making that really bad mistake.
Stay out of the road, stay off people's cars, and do not break the law. If you can manage that, then your protest will be peaceful and respected. If you act like this, well, then people aren't going to listen.