The dreaded “chicken swing” often is a result of an improper backswing. Players in an attempt to “hit from the inside” roll the club to the inside (under the plane) in the backswing. This results in the downswing getting “over the plane” and coming “over the top” which makes the arms come into impact too steeply. This steep path creates the “chicken swing”.
The old saying ….” hands in and clubhead out” in the start of your backswing is exactly right. Feel like the hands stay in close to your thigh and your clubhead stays outside your hands in the backswing, this will allow the arms and club to drop into the proper path and promote the “hitting from the inside” pat. That will eliminate the “chicken wing”! Good Luck!