Attack and defense are one. Details and examples follow..
Naoki Ishikawa at young age demonstrating sen-no-sen.
Avoid and attack at the same time. The head just moving off seichusen
because of the hipmovement and positioning of the body.
In the video below I use shuto uchi to attack. I'm posting this because
it is important to realise that you attack his body. That doens't
only mean his face of upperbody, you can attack his arms as well.
In this case i'm attacking the tsubo (pressure point) just above the
elbow. His arm doesn't seem to like it....
The bodymovement is simultaneous with the shuto. This
means, that tanden is used to initiate the power for the shuto and
this also makes the shift of the body possible. The primary movement
in your mind should be the shuto uchi, the body will (should) follow.