Beyond the Physics of Baseball

Or, why you can’t keep your eye on the ball.

OK, kiddies, while many of you are gearing up for the Hot Stove exploits of Billy Beane, J. P. Ricciardi, and Theo Epstein, I’m here to push you away from all that. The off-season is a great time to sit back and refresh your memory about more basic aspects of baseball, such as "does a curve ball really curve?" and "where is the center of mass in a baseball bat?"

Did I say "basic"? Well, maybe not—especially for you liberal arts majors out there in the roiling crowd. "Elemental" might be a better choice. The issues tackled by Robert Watts and Terry Bahill, engineering professors by day, co-authors of Keep Your Eye On the Ball: Curve Balls, Knuckleballs, and Other Fallacies of Baseball (Freeman, 2000) by night, cover some of the same ground familiar to many of you in Robert Adair’s The Physics of Baseball, but it’s clear from the get-go that these two guys aren’t going to provide us with a lofty, dispassionate tome. Keep Your Eye On The Ball is a lively, freewheeling effort that makes sense even though it’s packed to the brim with scary equations.

Interestingly, the authors come to some different conclusions than Adair, whose book has become something akin to the Bible for what we might call "applied baseball engineering." Adair’s measures indicated that a curve ball did in fact curve, but that the actual distance (deviation) of the ball was far less than what the batter perceived—only a bit more than three inches. Of the course of three chapters discussing the origin and impact of forces on a thrown baseball, Watts and Bahill conclude that rotation rate is the key element in determining the "break" (deviation) on a curve ball. Since the average major league curve ball has a rotation rate of 1900 rpm (or about 16 rotations in the time it takes to travel to home plate), the "lateral deflection" is closer to two feet.

But that’s hardly the most startling research finding to be found here. That comes from the work described in Chapter Seven, "Baseball Players Cannot Keep Their Eye On The Ball." Before we get too deep into the ramifications of this, let me tell you that this chapter will provide many of you (even some of the more noted science jocks here) with some fascinating information about the measurement of eye movements. In fact, it will provide many of you (and especially the liberal-arts types) with a whole new understanding of how the human eye works. (Pardon the digression, but a good bit of this is relevant to how Watts and Bahill came to their startling conclusions.)

They begin:

The velocity of a pitch approaches 100 mph. Tracking such a ball as it crosses the plate would require head and eye rotations in excess of 1000 degrees per second: a century of scientific research says that humans cannot track targets moving faster than 90 degrees per second. Yet major league batters manage to hit the ball with force consistently and are able to "get a piece of the ball" in 80 percent of their swings.

How is that possible? As Watts and Bahill explain, it’s due to the fact that four eye movement elements are integrated into the process of hitting a baseball. These are: saccadic eye movements, used in reading text or in scanning a roomful of people; vestibulo-ocular eye movements, used to maintain fixation on an object during head movements; vergence eye movements, used when looking between near and far objects; and smooth-pursuit eye movements, used when tracking a moving object.

You’ll have to read the entire chapter to get the full picture of how the measurements were performed (and don’t miss the photo on page 173 in which Bahill, rigged up with the special eyeglasses used to perform the tests, looks disturbingly like Bud Selig), but the surprise finding was that professional ballplayers move their heads when getting ready to swing at the ball.

It is this head movement that separates the professional player from the rest of us. As a result of this carefully controlled movement (more fully explained on page 180), pro players can track the ball an average of an extra 3 1/2 feet closer to the plate.

As Watts and Bahill point out, such a finding violates one of baseball’s fundamental hitting rules—"don’t move your head!" Their measurements indicate that the amount of movement made by the pro player was small—no more than 20 degrees—and probably would not be discernible by a hitting coach.

After this head realignment, batters use their saccadic eye movements to anticipate the final pitch location even as they are swinging the bat. (This is referred to by Watts and Bahill as an "anticipatory saccade," a term that it’s safe to say will never be uttered by a baseball broadcaster—not even Tim McCarver.)

All of this complex discussion reinforces and enriches the simple catchphrase that we’ve all uttered at one point in time: "hitting a baseball is the most difficult feat in all of sports." The value added to one’s knowledge from this book is that when you put it down, you’ll have a much better idea why this is the case—and that will serve to keep your mind off the machinations of GMs for an extra 3 1/2 seconds (maybe—that’s still subject to measurement, of course).

One caveat: Keep Your Eye On The Ball is book-ended by a set of opening and closing chapters that really don’t belong in the book, and demonstrate that the authors are probably not at all familiar with the tenets of sabermetrics. Bypass these two chapters, and you’ll be much more content with the contents herein. GMs (and those rehearsing nightly for the role, either in real life or on TV…) may find the visual testing methods described in Chapter 8 worth exploring and possibly even implementing: it’d be fascinating to discover the specific, hitting-related visual acuity of Barry Bonds vs. Rey Ordonez—and if a wider set of studies on hitters showed a solid correlation between that visual acuity and hitting success, current scouting methods might undergo a drastic change.