When you're playing as D.C. Carter in The Getaway, and you don't have your guns out, if you go up behind someone and press X you will subdue them and cuff them. The funny part is, you can do this to random passers-by on the street, and they will wind up cuffed and unconscious. Go up and try to arrest another cop this way, though, and it will have no effect.
If you do have your gun out when you do this, instead of cuffing the person, you will bop them on the head with the gun and knock them out. When attacking the gang members, this is better because it doesn't take as long.
It makes me laugh every time D.C. says "don't mess with the filth!" Maybe it's because this particular slang doesn't exist in American English. It's just funny somehow.