The pros hit the ball unbelievably low. They “cover” the ball with their chest (and clubface) through impact. They do this by keeping the left arm against the body and moving their chest through impact: the arms “tag along” and the wrists snap at impact, resulting in a “pinch” and a low, boring trajectory with a lot of spin.
We’ve all seen Vijay Singh hitting balls with a glove tucked into his left armpit. He does this to help him keep his arm “attached” to his body. If his left arm moves away from his body, the glove falls out. Chris DiMarco, as part of his pre-shot routine, folds his sleeve into his left armpit to force the same swing thought (his is course legal; Vijay’s is not).
If you’re having trouble keeping that arm attached, try sticking a glove in your left armpit – and keeping it there – throughout the swing.