Cure coming over the top

by Matt
(Houston,Texas, USA )

At the top of my backswing I have a problem with my club coming over the top like a baseball swing. I cannot get left wrist to stay flat. If I try to make it stay flat my swing feels out of wack, if I can even hit the ball. My stance and set up are fine. My club head stays online all the way to the top then my left wrist breaks. Is there anything I can do or practice to keep me from doing this. Thanks