You could let go of the bat when it strikes the ball and the ball
would still go as far as it would if you kept the bat in a death grip. Of
course, the infielders and fans might not like you very much, as they dive
out of the way of your flying bat. But as far as the ball is concerned,
you might as well let go.
That's because the time during which the bat and ball are actually in
contact, and therefore, the time during which one can influence the other,
is amazingly short-the entire collision is over in about 1.5 milliseconds
(for comparison, the blink of an eye lasts 100 milliseconds). It takes at
least 10 milliseconds for the information that you've hit the ball to travel
the length of the bat to your hands and then be transmitted along your nerves
to your brain. By the time you're aware the impact has occurred, the ball
is already long gone.
As a player, there's nothing you can do during the period of contact
to affect the ball; it's physically impossible for you to react fast enough.
All you can do is make sure your swing is the best it can be before you
hit the ball. And don't let go before the bat comes into contact with the
ball; then you'll lose energy, not to mention control. How far the ball
flies is determined by how fast the bat is moving when it hits. It doesn't
matter how hard you grip the bat.