...What would be the judicially acceptable adjective ...
How about this... "Once you have decided that you have no alternative but to defend yourself, and the time for action has arrived, you must act in a forceful and decisive manner. Be vigorous, and without hesitation."
That is how an animal would act. When I stumble upon a deer while hiking, it stands completely still, until it has decided it must move... and then IT MOVES. Small mammals like rabbits and chipmunks are even more impressive in their ability to go from frozen to explosive speed in the blink of an eye.
But what I said sounds so much more civilized than "go animal". Appearances count, even when they shouldn't.