The ball landed in the hardpan with a top layer of workable sand.
The sand is shallower, coarser, or wetter than the type of sand that you are used to playing in.
The ball landed in the short grass but the ground is incredibly hard. Because it is windy or you have plenty of green to work with, or you just want more control, you have decided to keep the ball low.
The ball landed in the short grass but the ground is incredibly hard.
The ball is resting on very short grass or mostly dirt.
An uncontrolled swing from a hardpan lie causes you to slice, hook, or hit the hardpan instead of the ball.
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.
You need to pick the ball up cleanly off of the surface of the hardpan.