First video, cop did the right thing. I probably feel he was getting physically tired and had just enough left in him to punch the girl and take her into custody. Had he grabbed her arm and twisted her around to cuff her he would have been placing his back to the other girl in black and thus leaving his weapon exposed to be grabbed by the girl in black.
Second video, the cop should have allowed the girl to make her phone call. He obviously turned the camera off and beat her because she was being defiant.
EDIT. If that were Renee punched in the face that hard because of her prior surgery she would be dead. This is something that every officer needs to keep in mind, physical force is sometime necessary BUT the individual may have a condition where normal physical force just to prove who is in charge may end up killing someone. I am sure there are people who wouldn't have a problem with that on their conscious but I would hope that it's only a few people. To the officers on this board please keep that in mind when physical force is necessary.
Third video, the off duty cop should have been let go. The on duty officer was obviously pulling him over using the fishing technique that other officers here have said they use. Once he informed the on duty officer that he was an off duty officer he should have been on his way, HOWEVER the on duty officer was a FOOL for allowing him to go back to his car to get his ID KNOWING that he had a gun. IMO that was a huge mistake and could have cost him his life if he was in fact not a cop and had a shot gun in the car.