FEATURE ARTICLE
Predicting a Baseball's Path
A batter watches the pitcher's motion plus the spin on the ball to calculate when and where it will cross the plate
A. Terry Bahill, David Baldwin, Jayendran Venkateswaran
A Catalog of Curvatures
Even more options arise when it comes to a curveball. First, a
pitcher grips the ball with his middle finger lined up along, or
just inside, one of the seams where the leather makes a roughly
circular shape on the surface of the ball, and his index finger lies
right beside the middle one. In general, a pitcher rotates his wrist
as the ball is released to throw a curveball. This causes four seams
to appear per revolution if you could watch the ball from directly
in front as it heads toward the plate; thus this pitch is also
generated by a four-seam grip. The index and middle fingers roll to
the front or side of the ball, imparting greater spin. An overhand
curve produces topspin, resulting in a downward deflection usually
referred to as a "drop." In other words, a ball drops more
than it would due to gravity alone. If a pitcher applies spin with a
vertical axis, as on a toy top, the ball curves horizontally, and
concurrently falls due to gravity. This "flat" curve is
thrown by pitchers using a sidearm delivery.
Most pitchers adopt what is called a "three-quarter
delivery," swinging the arm through an arc that is roughly
halfway between vertical and horizontal. This applies sidespin and
topspin components to a curve. For a right-handed pitcher, the ball
curves diagonally from upper right to lower left. The speed of a
curveball varies from around 70 to 80 miles per hour, and the spin
rate has been measured at up to 2,000 revolutions per minute.
The drop in a curve usually gives a hitter more trouble than the
sideways deflection, because of the shape of the bat and the
horizontal orientation of the swing. A bat's sweet area—the
place that can hit a ball most effectively—is about 4 inches
long but only one-third of an inch high. As a result, a vertical
drop is more effective than a horizontal deflection at taking the
ball away from the bat's sweet area, because the batter has a
smaller margin of error vertically. On the other hand, a horizontal
curve can be just as hard to hit as a dropping one when thrown to a
batter of like handedness—that is, right-hander to
right-hander or left-hander to left-hander. Anyone who has stood in
the batter's box—even facing a good high school
pitcher—soon learns that it is easier to hit a curve that is
deflected toward you instead of one bending away. Apparently, the
batter finds it harder to judge the horizontal location of the pitch
as it curves away. Also, a batter tends to flinch a bit from a
curveball that is aimed at him and then "breaks" toward
the outside corner of the plate.
Another horizontally deflected pitch is called a "slider."
It travels faster than a curveball, but spins less and,
consequently, only deflects about half as much as an ordinary
curveball. A pitcher throws a slider somewhat like a pass in
football. He takes a fastball grip and rolls his wrist slightly
during the delivery. That makes a pitcher's finger pass toward the
outside of the ball—sometimes called "cutting the
ball"—and that creates some lateral spin. A slider's axis
of rotation usually points up and to the left from the perspective
of a right-handed pitcher. This causes the ball to drop a little and
curve from the right to the left.
The curveball and slider bend away from the pitcher's throwing-arm
side, whereas a screwball deflects the other way. That is, if a
right-handed pitcher throws a screwball, it curves toward a
right-handed batter. In the early 1900s, Christy Mathewson—a
longtime New York Giant and member of the Hall of
Fame—developed this fadeaway pitch. One of Mathewson's biggest
rivals, Hall of Famer Mordecai "Three-Fingered" Brown,
threw a natural screwball because he lost part of his index finger
on his pitching hand in a farm-machine accident when he was a child.
In the 1930s, New York Giant Carl Hubbell made the screwball popular
once more. Of the pitches described in this article, pitchers throw
the screwball the least. It requires difficult twisting of the hand,
forearm and elbow that puts the pitcher's fingers on the inside and
top of the ball at the point of release.
No matter which way a curving pitch goes, once it starts to move, a
batter can predict the trajectory with some confidence. Not so with
a knuckleball. A hurler grips this pitch with his knuckles on a
smooth part of the ball or his fingertips dug into a seam. Then, he
holds his wrist rigid, basically pushing the ball, which reduces any
spin. This pitch travels slowly—only about 60 miles per
hour—and a good one revolves less than one time on its way to
the plate. That spin is unpredictable, as is the ball's trajectory.
For example, Hoyt Wilhelm—a Hall of Famer who was one of the
greatest knuckleballers—threw a knuckler that was described as
following a corkscrew path, attaining multiple deflections during
its flight.
Tricking a batter, though, takes more than throwing the right
curves. Changing the speed of pitches also plays a large role. Even
if a pitcher could throw 100-mile-per-hour fastballs for nine
innings, major league hitters would time the pitches and turn
potential strikes into home runs. So, pitchers also use a
change-up—just an off-speed straight pitch—that can be
thrown in several ways. One of the most common change-up techniques
is the palmball, which is thrown by shoving the ball into the palm
of the pitcher's hand. This reduces the whipping action of the
wrist, and even with a fastball delivery the velocity of the pitch
drops to 60 or 70 miles per hour.
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