CORRECT GRIP PRESSURE
Try not to strangle the club.
We need a certain amount of rotation in the arms during the swing and adequate movement in the wrists to carry out their role. Too tight a grip can prevent mobility in both the wrists and forearms.
Instead focus on key pressure points. Apply a little pressure with the three fingers nearest the butt of the club, the thumb beneath the pad on the left hand and also the forefinger of your right hand as it pushes against the shaft.
A thought I give to many of my students is that they are holding a small bird, don't crush it but do not let it fly away.
With this thought and sticking to the key pressure points it will eliminate any unwanted movement of the club in the hands at the top of the swing.