Select a length of pipe slightly longer than the length of your bat, and with a circumference slightly larger than the barrel of your bat. Take your normal stance, and have a helper stand behind you. Caution: the helper must stand far enough away in order to not be struck by your follow-through as you swing. The helper places the hollow pipe over the top third or so of the bat, and the helper and the pipe remain motionless.
As you swing, the bat should exit the pipe without making contact with the sides and without being impeded in any way. If your bat strikes the pipe or encounters resistance, you are not taking your hands forward toward the pitcher. Instead, you are looping the bat out and away in a slow arc – this is not an efficient swing.
Work on a fast, direct, straight-forward initial swing and enhance your bat speed while increasing the likelihood of a hit. Use this simple tool, and this simple drill, as a convenient pipeline to greatness.
From May 2011, http://raisingahitter.wordpress.com