A lot has been written about the need for a stable trail hip, trying to load a weak trail hip typically causes excessive internal rotation and adduction of that hip, perhaps a pelvic shift towards it, a.k.a sway. And maybe even elevation on that side and lateral bending of the torso towards the target in a desperate effort to maintain balance, a.k.a reverse pivot!
The position your trial leg is in at address is the position it should remain as you rotate in the backswing. Loading into the trail side leg, without over rotating the pelvis, requires stability in that trail side hip. If you have good hip stability it will allow you to turn without any sway. You will also be able to keep your centre of pressure within the inside of the trail side heel, this is important as it enables efficient use of ground reaction forces. Vital as, in the golf swing, we use the ground to create a coil so we can unwind the club with maximum force into the golf ball.
If the trail hip is unstable it may cause you to sway, which can lead to poor shot dispersion and a major loss in power.
Now take a look at the picture on the right. It shows Jordan Speith’s impact position (on the left) compared to a typical amateur golfer (on the right) what differences do you notice? Yes Jordan has definitely rotated more through impact, but what has allowed him to do that?
Notice how much more of his front foot you can see, his hip hasn’t come across covered it as it has for the amateur, he is able to this as his lead hip is stable and therefore provides a solid platform for his upper body to rotate. Indeed force plate analysis research suggests centre of pressure moves hard to target side in transition, a stable lead hip is vital to to provide a solid platform for that centre of pressure change.
To properly transfer force that is developed in your backswing, you need a strong AND stable lead hip. This lateral movement of the hip for the amateur, a.k.a slide, is a major power leak.
Also don’t forget the body has internal regulations to avoid injury. If the lead hip can’t stabilize the force in theory your body won’t allow you to develop the force either. Not to mention a slide can also create a ‘reverse C’ spinal position through impact and follow through which places the lumbar spine at greater risk of injury.