Slowing down with the upper body is easy. Stop TRYING to move your upper body. It's automatic. Both the moving AND the slowing of the upper body.
Stand still in the athletic position, weight neutral, reach back. Let the twisting of your upper body move your hips. When I do this, the hips BARELEY point back, just a few degrees. Now, shift your weight to the back foot, while keeping that tight, twisted feeling through your side, and the back of your shoulder, NOW you will feel your hips rotate back. From here, it's just a matter of pushing with your back foot and shifting your weight forward (with your lower body) to get your hips to turn 90 degrees. 90 degrees is all you need, 90 degrees puts you in postion to aim, to crack the whip, to pound the hammer. What really helped me at this point was to *almost* make an effort to NOT let my upper body come around. When you feel the tug, just relax and go with it. Viola, the upper body comes around to the 90 degree position and you can use that momentum alone to sling your arm forward in whip like fashion.
I don't know if I would call this a drill, but this is what I do whenever I feel like I am over turning with my upper body, or just not getting any lower body power.
Hope it helps.
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