Rotational movement is any type of movement in a circular motion. Ultimately, it is this type of motion that generates the speed and power hitters need. Once the hitter strides to his balanced position, he needs to rotate his hips towards the pitcher. Another way of feeling this motion is to turn the belly button towards the base line—first base for a left hand hitters and third base for a right hand hitters.
When you engage in this motion correctly, you will notice that this rotational movement will pull your hands into the hitting zone. This illustrates a key principle with hitting: the hips are indirectly attached to the hands. As the hips rotate, they pull the hands into the hitting are, causing the knob of the bat to be pointed at the ball.
As the lower body rotates and opens up, it is important to keep the upper body closed. This creates maximum torque, which generates power. Torque is a fancy word that means nothing more than two forces working in opposite directions. As the lower body rotates, the upper body resists.
This type of motion is scientifically proven to produce the maximum amount of speed and power. When hitters get themselves into this type of position, they have the momentum of the biggest and strongest muscles in the body (the hips and thighs) pulling the smaller and weaker ones (the hands and arms) through.
Despite the scientifically and biomechanically proven results of this torque position, many hitting instructors still teach their pupils to “squish the bug.” The term squish the bug is a theory of hitting that encourages hitters to use their feet to rotate their hips. The back foot, by turning it after the stride, causes the hips to turn.
Though this theory can be done, you have to be an incredibly gifted athlete to coordinate your feet, hips and hands. Secondly, the turning of the feet often causes hitters to spin, rather than turn. This spinning action results in the hips prematurely turning and the shoulders flying open, causing the hitter to pull off the ball. This ultimately prevents the hitter from covering the plate consistently, in particular the outside corner, as well as adjust to curve balls and off speed pitches.
Most importantly however, squishing the bug does not lead the hitter into a powerful baseball hitting position because the turning of the back foot does not facilitate torque. Ultimately, starting rotational movement with the turning of the back foot results in smaller and less powerful muscles (the feet) leading the more powerful muscles (the hips and the thighs).
Nowhere in the study of biomechanics does it state that more power and speed are created by smaller and weaker muscles leading larger and stronger muscles.
If you were at a monster truck derby, which situation would create more speed and power—a truck pulling a small car or a small car pulling a truck? Obviously, the truck pulling the small car creates more speed and power.
The key to maximum batting speed and power is the hips leading the hands and the feet, not the other way around.