From personal experience: The police will put you in back seat and they will prevent your head from striking the door jamb when they do. If you are resisting, then your head might connect with the door jamb “accidentally”; but the cops will rarely risk a brutality beef in their jacket,especially if they are career-oriented and looking to advance.
There’s also the facts that:
[li]Most departments have cameras in squad car recording arrests - If you are roughed up, it can make valuable evidence go out the window as the footage would have to excise the portions where the police assaulted you.[/li][li]Cops often tell on other cops - To make certain that they don’t take any of teh weight for a brutal asshole, cops will rat out an officer who roughs up suspects in their presence. Thin Blue Line or not, nobody wants to endanger their job or their pension for someone who can’t control himself/herself.[/li][li]Many arrests take place in front of witnesses - You rough up suspects unnecessarily in front of witnesses, you are risking your badge. Most cops won’t risk that just to teach someone they dislike a “lesson”, especially in front of witnesses.[/li][/ol]
I’m not a big fan of the police for a wide range of reasons. However, I have never seen one intentionally hurt a suspect who they ere placing in a vehicle.