A Sway is defined as any excessive lower body lateral movement away from the target during your backswing that forces your weight to the outside of your trail side foot. This swing characteristic makes it very difficult to develop a proper weight shift during transition and the downswing. Imagine a baseball batter digging in at the plate with their back foot. This simple routine allows them to coil around their back leg and drive their weight from their back leg to their front leg in a very efficient manner. If there is no stable platform to drive your weight off of during transition, you will lose power and try to develop speed in an inefficient sequence.
Physical Parameters Causing Sway and How to Diagnose Them:
In order to coil around your right hip (for right handed golfers) during the backswing several physical characteristics must be developed. First and foremost, right hip internal rotation is paramount for full rotation into the right hip without any lateral sway. If the body is unable to rotate around the right hip due to joint or muscular restrictions than lateral movements will dominate the pattern. Secondly, the ability to separate your upper body from your lower body allows the lower body to laterally stabilize while rotating during a large shoulder turn. Limited trunk to pelvis separation is usually caused by reduced spinal mobility and shortened lat flexibility. Finally, the ability to laterally stabilize your right leg during the backswing is directly proportional to the strength and stability of your gluteal musculature (your butt). When it comes to lower body lateral stabilization the glute medius is the king. This muscle helps prevent the right hip from elevating and shifting lateral during an aggressive coil into the right hip.