The rule in question here is as follows:
It might benefit from a clarification since the attempt officially starts once the bar leaves the rack and finishes when the bar goes back into the rack. What we mean here is that your hands cannot move during the down-up portion of the squat. It is generally a bad idea to move your hands once you have unracked the bar, but if you are using equipment that necessitates that your move your hands as you step back, or step into the rack, that will not be cause to red light you. Several of the locations will be using adjustable combo racks that permit the stand arms to slant inward. This allows for a hands-at-the-collars grip, obviating this problem.The bar must be held horizontally across the back with some part of both palms above the wrist in contact with the bar. This position, once fixed, cannot change during the attempt.