Developing a smooth and consistent swing is the goal of anyone who has ever picked up golf clubs. It takes time and effort to get to the point where your swing is grooved and you don't make basic errors. One of biggest problems is hitting behind the ball, which is also known as "hitting it fat." This problem often happens when a golfer is trying to be too careful with his swing and he wants to make sure he does not top the ball. There can be other factors as well.
One of the reasons for hitting behind the ball is that you are trying to assure you will get the ball in the air by swinging up at the ball. This is often the case with new or high-handicap golfers. To swing up at the ball, you have to start your swing from below the angle of impact. If your timing is anything but perfect, you will hit the ground before you hit the ball, causing you to hit the ball fat and slowing down your clubhead at impact.
Playing the ball too far back in your stance can cause you to hit the ground behind the ball and keep you from getting the accuracy and distance on the shot that you want. Playing the ball further back in your stance can be useful at times if you want to make sure your shoulders stay closed and you want to punch the ball to the target. But playing the ball too far back will very likely cause you to hit behind the ball, and the result will be a poor shot.
Lack of Hip Rotation
A full and complete swing involves rotating the hips during your downswing. Many golfers fail to either turn their hips or turn their hips completely through the ball. Think of it as a baseball swing. If you are a right-handed power hitter, you want to hit the ball into the left field bleachers. That involves turning your hips as you make contact. In golf, you must turn your hips if you want distance and accuracy on your shot. If you don't, you will likely hit the ground before you hit the ball.