A fat shot occurs when the club hits the ground too soon, creating a cushion of dirt and grass in-between the clubface and the ball, essentially killing the shot.
Diagnosing Fat Shots
Not normally a factor with fat shots.
Your weight might be too far to the right and/or your right shoulder might be too low at address. Your aim could be too far to the right.
The ball might be too far forward (toward the left foot) in your stance.
You might be taking the club too far inside, away from the target line. Your posture should remain the same without leaning toward the ball or lowering your head.
You might be too far to the right on the downswing. Keep your posture without lowering your head toward the ball. Shift your weight! You should have some 80-percent of your weight on the front foot at impact.