The head will remain perfectly still as the body rotates under it. Forces from the ground up will cause the knees, hips and shoulders to rotate as if they were in a cylinder. It is important to remember that rotation around a stationary axis is generated from the ground up. The rotation of the hips and torso comes mainly from the action of the legs, knees and feet. Rotation is not generated from the actions of the arms or swinging of the shoulders.
Rotation is the power source of a great hitter.
But having the power isn't worth a dime if you can't efficiently transfer it. Yes we do hit off of a fairly straight front leg. The lead knee and leg rotate and straighten to drive rotation of the hips and body. Display summaries of other articles about hitting . Search the Web.