When attempting to put a lot of backspin on the ball so that it stops, or even backs up, when it lands on the green, often it is said to "pinch" or "squeeze" the ball between the club and the ground.  While that may be what it feels like, that cannot really be what happens.

Recognizing that the ball can only receive an input force perpendicular to the clubface (that is much more significant than the frictional force along the clubface) it is not possible for the ball to be "pinched" or "squeezed" by the club with the ground (unless it is hit with the bottom of the club - "topped" - in which case it won't fly at all).  The loft of the face of the club (particularly a wedge) is oriented upward, so the ball will immediately depart in an upward direction rather than with any motion toward the ground.  This will occur regardless of the direction of the club.  Even if the club is moving downward significantly, the force at impact sends the ball in the direction perpendicular to the clubface.  The downward motion of the club can work to enhance the spin, which is really what needs to happen in order to produce significant backspin, but the ball will not be pinched with the ground.

A way to pinch the ball between the clubface and the ground would be to deloft a low lofted club so the clubface was oriented with a slight downward angle.  The result of this would be to hit the ball downward into the ground and it would not fly into the air as there would be no upward influence on the ball.

Consider further that if the ball where pinched by the club with the ground, that the friction of the ball with the ground would inhibit the ball's spin, which is counter to the intended shot.  Slow-motion video of a golf club hitting a ball clearly shows the ball rising perpendicular to the clubface upon impact and not having any possible downward motion.  For the very short time that the ball is compressed and in contact with the club, it rolls up the clubface, initiating spin.  The grooves on the clubface enhance the friction between it and the ball to impart backspin to the ball while the ball rolls up the clubface.

Increasing the downward angle of the club at impact should increase the spin, but for the same club velocity, more downward speed means less forward speed and less force transferred to the ball, so to maintain distance the ball must be struck with the club moving even faster to produce the same forward speed.  The increased downward motion will promote spin, and hitting the ball harder generates more compression on the ball which will enhance the transfer of friction from the club to the ball, thus generating more spin.  The additional compression is likely the feeling that is transferred up through the club to the player that is commonly referred to as "pinching" the ball with the ground.

So, while the dramatic downward action of the club produces the intended result of more spin, the reason does not include squeezing the ball with the ground.  Perhaps the mental notion of trying to pinch the ball with the ground helps a golfer produce a more downward action that has the result of creating more spin, but the physics do not back up the explanation as a reason, and with real understanding of the circumstances, perhaps the intended result can be achieved more directly.

An excellent example of a wedge hitting a golf ball can be found here.

The important moment occurs at 0:23.  The ball immediately takes off in an upward direction nearly perpendicular to the clubface.  Notice the downward path of the club that continues down after hitting the ball and causes a large divot to be taken after striking the ball.  Spin is generated by the direction of the club being closer to parallel to the loft angle, and in order to produce forward force, the ball must be hit harder as the club direction becomes closer to along the parallel to the loft of the club.

There are many videos and explanations available online, and the purpose of GolfMystique.com is to help discern which are helpful by explaining the rational physics pertaining to golf.  With correct knowledge, any player can determine what information is valid and how it can help them.