ASEE PRISM - October 2000

Professional baseball players are hitting more home runs than ever before, and major league officials have called in an engineer to determine if the ball is to blame.

By Ray Bert

photo courtesy of Major League Baseball PhotosAbout a week into the 2000 season, a batter for the Los Angeles Dodgers strode to the plate at San Francisco's new PacBell Park and slammed a two-run home run over the fence. No big deal, right? Well, consider that it was his third homer of the game. Then consider that the hitter wasn't the hometown Giants' Barry Bonds, the Dodgers' Gary Sheffield-or any other big-time power hitter-but Kevin Elster, the Dodgers' journeyman shortstop who didn't even play the previous season, and who had hit only 86 home runs in his 12-year career.

Elster's heroics in that game-in which 6 homers were hit in all-may have seemed an aberration, but across the major leagues the numbers and the improbable feats piled up throughout the season-ultimately adding up to a power surge of historic proportions. Mark McGwire's 1998 record of 70 home runs still stands, but it is one of the few homer-related stats that didn't break new ground.

As of late August, home runs per game had reached an all-time high of 2.41, eclipsing last year's record of 2.28 by 6 percent, or nearly 400 homers over the course of a season. Theories abound for the surge in homers, including stronger hitters, smaller stadiums, and weaker pitching as a result of expansion, which has added four new teams in the 1990s. But there are some who point to the ball itself, charging that it has been intentionally "juiced" to produce more crowd-pleasing-and not incidentally, courtesy of Major League Baseball Photos

Others disagree that any such plot is afoot, but still contend that modern manufacturing methods have turned baseballs into something more similar to a golf ball. The Rawlings company, makers of the official major league baseballs since 1977, insists that the ball has not changed. But with so many players launching shots worthy of Tiger Woods, how can you know for sure?

Enter Jim Sherwood, director of the Baseball Research Center at the University of Massachusetts-Lowell. In April, with Elster and nearly everyone else already homering at an alarming rate, Major League Baseball asked Sherwood-a professor of mechanical engineering and an ASEE member-to determine whether this season's balls are somehow different from previous years. For several months, Sherwood weighed, measured, and cut apart baseballs to determine whether they met the specifications in the sport's official rules. The pivotal measurement is the coefficient of restitution (COR) test, which measures how hard a ball will rebound from a collision. Major League Baseball specifications call for a rebound velocity of roughly 54.6 percent of the original speed, plus or minus 3.2 percent.

To determine the COR values, Sherwood used a machine that swings a bat at a speed of 70 miles per hour to hit a baseball mounted in Styrofoam, which is used to ensure a consistent striking point-important because balls hit on the laces will react differently and more unpredictably. Sherwood measures the speed of the batted ball at three different spots using photo cells, in which the balls break a beam of light at a known distance and a measured time after impact.

photo courtesy of Major League Baseball Photos   

Enron Field
photo courtesy of Major League Baseball Photos

Shrinking Stadiums

A dozen new baseball stadiums have opened since Baltimore's Camden Yards debuted in 1992, most of them with smaller field dimensions than their predecessors. Houston's cavernous Astrodome--billed as the Eighth Wonder of the World when it opened in 1964--was replaced this season by the much cozier, and more homer-friendly, Enron Field.

So what did Sherwood discover? In short, he found no significant difference between the 1999 and 2000 baseballs, though he did determine that the tolerances for some specifications should probably be tightened. While the balls tested were fairly uniform and would travel just a few feet more or less in a game, Sherwood says that the specifications are such that two perfectly "legal" balls-one on the light side and harder, the other heavier and softer-could vary in batted-ball distance by as much as 49 feet.

Despite conclusive evidence that baseballs themselves are not the reason for this year's jump in home runs, Sherwood's findings-which apply only to the last two seasons-do not wholly settle the juiced-ball controversy. Home runs have been increasing steadily for most of the past decade, not just this season. Moreover, the study showed that the balls, though within specifications, have COR values toward the higher end of the acceptable range-and no one yet knows for how long they have been that way. Testing older balls would be an obvious solution, but there aren't many available that have been stored in the controlled temperature and humidity conditions necessary for valid tests.

Jimmie Foxx                   Frank Thomas

Bigger and Stronger

In his heyday in the 1930s, the 6', 190-lb Jimmie Foxx was known as "The Beast" because of his unusual size and strength.
The 6' 5", 270-lb Frank Thomas ---"The Big Hurt"--- is now our idea of an oversized ballplayer.

Sherwood hasn't always been the technological point man for America's pastime. He was previously involved with research on automobile impacts in collisions. It turns out that the collision between bat and ball is not all that different, he says. A die-hard Indians fan, Sherwood calls the work "a fantastic opportunity laid at my feet," and notes that it has applications for his teaching since coefficient of restitution is a concept taught in dynamics classes that most engineers take. Sherwood also supervises both master's and Ph.D. students at the Baseball Research Center-including one whose work with the NCAA and Major League Baseball on bat performance led to the creation of the center.

Despite his interest in the game, Sherwood hadn't given much thought to the reasons behind the  hitting phenomenon until he got involved with the study. Now he suspects that bats may play a big part. It seems that hitters have been doing a little engineering design work of their own: "Hitters modify the profile of the bat [by sanding or shaving] to increase their swing speed," which may be causing the ball to travel farther, Sherwood says.

Another engineering study of baseball-and more controversy-may be on deck.

Ray Bert is senior editor of Prism.

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