Lack of flexibility in the hips causes you to straighten your spine and bring your pelvis underneath your body on the backswing
The baseball swing is very similar to the golf swing and you can get a great feel for the backswing, downswing and follow through by making baseball swings above the ball and then hitting the ball with your golf swing
The roll of the right leg in the swing is very misunderstood in golf, it is extremely important for control and distance, as the club comes into impact the right knee, foot and ankle roll in and at the finish the right thigh should catch up with your left thigh