The girl put in the car is a teenager I believe... If I remember correctly she was walking home from school and j-walked. BUT how it all went down is the cop had a male for j-walking 1st (the guy in the blue/green shirt?), the cop seen the 2 girls do the same thing and called them over for a ticket as well. The 1st girl that was not hit, said many "wrong" words to the cop, so it started she was going to get arrested for her mouth (what ever charge it would have been). Then girl number 2 interfered with the arrest and YES assaulted the cop that is why she was hit. IMO the force was needed and justified. After girl #2 went away licking her wounds, he was finely unable to get girl #1 under control, cuffed and put in the car. You don't see it in the video, but the girl that was hit was also arrested, her main charge was "assaulting a police officer". If she dose jail time and she should, then the cop should be good to go from any type of charge or lawsuit by her or her family. Because of the people watching this go down, I think the cop is lucky things didn't go much worse. This cop got backup soon after the video stops, but it took way to long.
I bet if that was a male this happen with, he would gotten much more then just one hand to the face, IMO the cop held good restraint not to pop her a few more times.
The sad thing is... Even if that video shows all that went down, he wont come out of this smelling like roses, in the least he needs some more training on cuffing (I am not saying a could of done better, I am not trained as a police officer).