When their hands go up defensively, the oc comes out. Their action plus one.I think the Army has it right when they call their system Combatives. My department still calls our proprietary system Defensive Tactics but being an instructor we drill new recruit officers and veterans alike that we do not wait for someone to hit or attempt to hit us in order to take action.
A small example of this is scenario training with a party who is passive resistive but begins either making statements about fighting/not-going to jail or rolling his hands into fists. If any of these take place and there is reason to go hands on then we can engage in an offensive manner. We do not wait until the other person is set to attack. I hear that Krav is like this as well. There is rumor that we will soon be calling our system Police Combatives but I will believe that when I see it.