We always say teaching pitching and hitting are the same. So, what is bat lag and how can it be applied to teaching pitching fundamentals? According to professional hitting coaches, lagging the bat helps create power in the swing. So what defines bat lag? Bat lag occurs when the front foot lands after the initiation of the stride and the back hip starts to rotate. The hands start to move but lag behind the hip move and are loaded behind the ball. The hands then explode to the ball with the maximum bat speed and power, creating full arm extension. The swing is finished off by a high follow through and full shoulder rotation. You can see the correct shoulder rotation on a right-handed hitter if you can spot the player's back or number from the first base dugout.
A lot of professional pitching coaches use the term hip/shoulder separation. We will use “shoulder lag.”
After the pivot to start the pitching delivery, the front leg is lifted. The front foot then lands softly, beginning the back hip action. No rotation occurs until the foot landing. When the back hip starts to rotate, the shoulders remain square and the back shoulder stays behind the baseball until the hip rotation naturally pulls the shoulders through the pitching zone. This movement creates a powerful and complete shoulder rotation and the correct finish to the delivery.
It is the same action as hitting: bat lag, shoulder lag.