What's the name of the martial art that is all flow - you don't strike back, but you don't put force against force, you just use their own energy to deflect? You're not striking back, but you're not ignoring it either and letting it smack you in the face.
I feel you are thinking of Aikido.
However it would equally apply to a majority of the so called 'soft styles' of which there are a whole number.
You go with the flow of the other, redirecting and guiding their own force rather than resisting it or meeting it head on.