This is just an observation from my own swing and from learning on these forums. I used to always have a cupped left wrist at the top...not on purpose, just didn't know any better. This was very hard for me to correct. From reading on here I heard the reason I was doing it was because I was cocking my right wrist. This didn't help me. Through experimentation and slow motion stop at the top swings etc, I have noticed the reason MY left wrist tends to want to cup.
My left wrist begins to cup when I overswing with my arms and hands. In other words when my chest stops turning, but arms keep on going. If I stop the arm swing when the chest stops my left wrist never even wants to cup and I can maintain the flat left wrist. When my arms get too far behind me, it is cup city. Realizing this has improved my game tremendously, just thought it might help someone else.
My left wrist begins to cup when I overswing with my arms and hands. In other words when my chest stops turning, but arms keep on going. If I stop the arm swing when the chest stops my left wrist never even wants to cup and I can maintain the flat left wrist. When my arms get too far behind me, it is cup city. Realizing this has improved my game tremendously, just thought it might help someone else.