This is especially important when facing multiple opponents because it’s not a good idea to stand still, root yourself, throw a punch or kick, and then look for another bad guy to hit. Chances are good that a bar stool will be broken over one’s head before a second (or first) punch is thrown. Being able to move and strike with authority, with ‘rootedness,’ is important in encounters because bad guys don’t travel solo.
Structure is comprised of the right body alignment; hips tucked, head reaching to the sky, shoulder over hips, knees and toes facing the same direction, etc.
Structure is comprised of proper movement; stepping (rolling step, immortal man step, etc.), turning (ba turn, night swallow turn, etc.), crossing the great river (the name of a concept where one does not become double-weighted and have all of one’s force applied to the hand, arm, elbow, etc. that’s on the same side as the supporting leg), breathing (proper breathing provides internal structure), and so on.
Proper structure is a complex set of body mechanics that when properly configured and set in motion, provides the same body rigidity as standing still, bracing with the legs, and punching or kicking. It’s quite a sophisticated set of body mechanics and a foundation of the art. All other aspects of JBG build on these concepts, so they are taught right from the get-go.