Importance of Checking Bat Speed at Contact
Most batting instructors would agree that there is a direct correlation between the velocity of the bat and how far a well hit ball will travel. Yet, two players swinging the same bat on about the same plane with comparable bat speeds may vary greatly in the power they display. One batter might hit balls well over 400 feet while the other would carry only 300 feet. This would seem to be contradictory until you take into account when the maximum bat speed occurred during the two swings.
The bat speed that really counts is that speed attained at (or by) contact. Swing mechanics of a great hitter allows him to generate higher bat speed much earlier in the swing than average hitters. Players with a lot of "pop" in their bat transfer all of the body's rotational and torque energies into bat speed before and/or at contact. After contact their limbs and torso will have expended their energy and are now in a relaxed and coast-out mode. The follow-through portion of a good swing is powered from the momentum of the bat pulling the arms and shoulders up and through.
Average hitters are still expending energy to gain bat speed for 20 to 40 degrees (poor hitters past 60 degrees) of bat travel after the bat passes the optimum contact point. Some coaches would contend that gaining speed after contact is beneficial because of the "driving through the ball" effect. --- The facts do not support this theory. --- The ball is in contact with the bat for about 1/2000 of a second. During this time the bat moves forward approximately 3/4 inch.
So once again, the important bat speed for determining a player's pop or power is the bat-head velocity attained by contact, not the speed attained later during the follow-through. When hitting off of a tee or a heavy bag, the Swing Speed Radar unit displays the bat speed reading at contact.