The Physics of Cheating in Baseball

Corked bats and juiced balls have long plagued baseball, but do they really help a player’s game? Four scientists found surprising answers

The issue of juiced baseballs surfaces every couple years during the month of April due to a high rate of home runs hit. (Ed Wolfstein / Icon SMI 756 / Ed Wolfstein / Icon SMI / Newscom)

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Smith summarizes it this way: “If your goal is to hit more home runs, you should have a heavy bat. If your goal is to have a higher batting average, you should have a lighter bat.”

Keith Koenig, a professor of aerospace engineering at Mississippi State University and a fellow baseball researcher, trusts the paper’s results but cautions that a bat-swinging machine can never fully predict what might actually happen out on the diamond when real batters swing bats. “If we allow corked bats in the Major Leagues, would there be more home runs?” Koenig muses. “That’s the kind of question that can’t be answered just from lab tests.”

Good Hitters—or a Juiced Baseball?

Every few years, during the month of April, Nathan says, batters start hitting home runs and the cry goes up: The baseball isn’t what it used to be! It must be juiced! (Why always in April? “Because in April there’s not enough data to be statistically significant…and people start to speculate,” Nathan says wryly.) The issue of juiced balls surfaced again in 2000 when the first two months of the season saw home runs hit at a notably higher rate than the same period the previous year.

To test the speculation that something had changed with the balls, the researchers compared the bounciness of balls from 2004 with a box of unused balls from 1976 to 1980. They shot the balls at a steel plate or a wooden bat at 60, 90, and 120 miles per hour and measured their bounciness after a collision—what physicists call the coefficient of restitution.

The result? “There was no evidence that there was any difference in the coefficient of restitution of the different balls,” says Nathan. One caveat: the scientists can’t say that balls made in other years aren’t livelier.

How times change, though: these days we’d more likely attribute a rash of home-run slugging to performance-enhancing drugs, not the ball.

The Humidor: Not Just for Cigars Anymore

Coors Field, home of the Colorado Rockies in mile-high Denver, is a pitcher’s nightmare and a batter’s nirvana. The air is only 80 percent as dense as air at sea level, and because there’s less air resistance, balls fly farther and pitches cannot curve as much. That means more hits and more home runs. For the first seven seasons at Coors Field, there were 3.2 home runs per game, compared with 1.93 home runs at the Rockies’ away games.

To try to discourage the mile-high bonanza, in 2002 the Rockies started storing game balls in a humidor that kept the balls at a constant 70 degrees Fahrenheit and 50 percent relative humidity instead of Denver’s typical 30 percent humidity. The idea was that higher humidity reduces the bounciness of the ball and slightly increases its weight. Indeed, the average number of home runs at Coors Field dropped 25 percent from 2002 through 2010.


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