So here's your definitive answer, from someone who does just what you're asking about:. . It's pretty much what everybody here has said. . . It's not what wazwondring says, and it's obvious all that movie-watching has taken it's toll. . . Drew25 is right on, also.. . As for motivation, abfabmom1 hits it right on, also. . . There's no "national standard procedure" for doing this, though certainly many agencies might well have a policy requiring their officers to do it when feasible. I do it for most of the reasons listed here and because I don't want the knucklehead (who is often drunk or drugged) to hit his or her pretty little head on the car. I have a certain obligation and responsibility to keep my prisoner from injuring themselves while they are in my custody, and this is one way I exercise that obligation.. . Also, and this will make some of the folks here happy to see, there is a certain amount of force that can be applied against someone when necessary to get them into a car if they don't want to get in. Having my hand on their head already makes it easier to apply that force if I have to. . . SEE?! HE ADMITS USING FORCE!. . Yes, I do. Necessary force. . . And usually, I don't actually put my hand *on* their head. I generally put the back of my hand against the part of the car they might hit their head on. That way, I don't have to get whatever gross icky stuff they have in/on their hair on my hand unless they are actually about to hit their head on the car. In that case, I've hopefully kept them from hurting their noggin and I can wash my hand.