What the Batter's Eye Tells the Batter's Brain

Terry Bahill

Dave Baldwin

Systems and Industrial Engineering

University of Arizona

Tucson, AZ 85721-0020

terry@sie.arizona.edu

http://www.sie.arizona.edu/sysengr/slides/eyeTellsBrain.ppt

http://www.sie.arizona.edu/sysengr/slides/rightHandRules.ppt

© 1998-2006 Bahill

For most pitches in baseball, the pitcher uses a two-seam grip or a four-seam grip. Pitchers often say that using a two- or four-seam grip causes the ball to move differently. When explaining baseball phenomena, we first use principles of Physics, then Physiology and finally Psychology. OK, Physics first. Most wind tunnel tests have shown little difference in forces between the two-seam and the four-seam orientation. The spin that the pitcher puts on the ball causes it to curve.

When a major league baseball pitcher is asked to describe the flight of one of his pitches, he usually illustrates the trajectory using his pitching hand, much like a kid or a jet pilot demonstrating the yaw, pitch and roll of an airplane. The hand used as an analog in this way is a gestural example of a somatic metaphor. We develop a sense of space and of the potential of action from the feel of the body as it interacts with the environment. Like other kinds of analogies, the somatic metaphor helps a modeler form a conceptual system to deal with the external world.

The right-hand rules form a pair of gestural metaphors that has been widely used for centuries as mnemonic or heuristic devices in science, mathematics and engineering. This pair comprises an angular right-hand rule and a coordinate right-hand rule. The spin axis of a pitch can be found by using the angular right-hand rule. If you curl the fingers of your right hand in the direction of spin, your extended thumb will point in the direction of the spin axis. The direction of the spin-induced deflection force can be described using the coordinate right-hand rule. Point the thumb of your right hand in the direction of the spin axis, and point your index finger in the direction of forward motion of the pitch. Bend your middle finger so that it is perpendicular to your index finger. Your middle finger will be pointing in the direction of the spin-induced deflection: mnemonically, Spin axis x Direction = Spin induced deflection (SaD Sid). The right-hand rules show the direction of the spin-induced deflection of baseball pitches. Thus, they explain the movement of the fastball, curveball, slider and screwball.

Physiological differences between the two- or four-seam grips allow pitchers to apply different finger pressures, which could produce small differences in spin axes and spin rates.

However, the greatest difference is Psychological, specifically the batter's perception of the ball. The ball's appearance to the batter is different for the two-seam and the four-seam fastballs. We skewered baseballs on bolts in the two-seam and four-seam orientations. The bolts were chucked in electric drills and were rotated at 1200 rpm. The speed of rotation was measured with a stroboscope. The 2-seam and 4-seam simulated fastballs look drastically different. Critical flicker fusion frequency offers a partial explanation. Because of the perceptual clues presented to batters, we advise pitchers to use the four-seam grip for fastballs and curveballs, but the two-seam grip for sliders.

References [85 and 89]. This seminar is suitable for engineers and even the general public: it has few equations. It requires PowerPoint and a computer projector. This talk takes about an hour.