Your ball lands on cement, asphalt, or gravel but is still considered to be inbounds.
You try using your sand wedge and end up skulling the ball when attempting to hit off of a thin layer of sand over hardpan, especially if the sand is wet, or scruff. This is because the ball bounces off of the flange of the sand wedge and you end up blading or chunking the shot.
Your ball lies in hardpan composed of hard-packed sand or dirt such as greenside bunkers where the club can penetrate the sand.
Decreased flexibility can prevent proper hip rotation and therefore power, causing you to sway during your backswing. This is a very common problem for senior golfers because their muscles tighten as they age, inhibiting a proper turn for a full swing.
The clubhead digs into the ground before contact, causing the ball to fly short. If your swing decelerates during your forward swing, it will cause your hands to fall too far behind the clubhead at impact and you will duff the ball.
Unsure if you need a high, mid, or low bounce or how bounce affects your game.
The ball is sitting in the front lip of the sand trap.
You need a lot of spin to help the ball land on a narrow green or a sharply inclined green. You might need just the opposite, less spin with extra roll because you are unable or it is unsafe to aim at the pin directly.
You have a buried or plugged ball in the sand trap.
You do not have the feel for pitching or are not very consistent at it. If you square your body to the target line, you will end up flicking your hands to help attempt to make clean contact.