Have you ever swung completely under a shot with a wedge around the green? 

What you are facing is a ball that is sitting up in the grass and not sitting firmly on the ground.  First, be careful addressing the ball. It could move.  Second, you always want to address the ball where the bottom of the ball rests.  In this case hold the club slightly above the ground so that you will encourage the club to strike the bottom of the ball and not under it.  Using this technique will stop you from going completely under the ball