I have changed to use the overlap grip this year and have been following instructions on how to grip properly.
From what I've read/seen it suggests that the thumb of the right hand (I play right handed btw) should be pointing towards the left foot.
However as I swung the club I would often tighten my right hand grip and the pressure and direction of the thumb would close the club face and cause snap hooks. I could feel the club closing on my downswing and eventually decided to move my thumb to pointing straight down the club face, I have swung better since BUT it doesn't feel quite as natural.
I thought that maybe my right hand was rotated too far down the club (i.e holding the bottom of the club), moving my thumb naturally forces it into a better position??