I've wondered this when I see videos of people getting beat into submission so the police can place handcuffs on someone. Is there any point where you can claim self defense against a claim of resisting arrest? Even if you should be arrested does that mean you can get beat on until your hands are behind your back?

When you are being beat on the natural reaction is to defend yourself, so it seems counter intuitive to beat someone with the expectation that they won't defend themselves and will place their hands behind their back. It just won't happen.