Regardless of the name, the purpose and the execution remain the same. This drill is unmatched at teaching a short, fast, efficient swing. Strict adherence to this drill eliminates a long, slow, sweeping swing.
A hitter stands facing a fence or wall or mirror or curtain. For safety, a curtain or hanging blanket is best for beginners. Hitter stands a few inches farther than 1 bat length from the fence, as measured by a bat held against his abdomen and extended toward the fence. Hitter takes his normal stance and faces an imaginary pitcher, as if the pitcher’s mound was parallel with the fence.
Hitter swings at imaginary ball, keeping his hands close to his body so as to not contact the fence with his bat. If the bat hits the fence, it is an indication that the hands are extending too far away from the body. This drill teaches the proper swing and offers instant feedback.
Note: until this skill is ingrained and habitual and exemplary, use an old bat in lieu of a new or game bat.
From October 2010, http://raisingahitter.wordpress.com