Coors Field, Denver Colorado

Coors Field, Denver Colorado


The Physics of the Colorado Rockies' Success

by Eliot Baker

The Colorado Rockies’ World Series run defied the odds of Vegas by observing the laws of physics. Major League Baseball leveled its playing field this year through creative utility of humidors—storage units that keep temperature and humidity constant. While operating a humidor might not be rocket science—they are like nine-foot-by-nine-foot refrigerators—their effect on baseballs more or less is.

“The humidor is a good example of a science-based change in baseball,” said Mont Hubbard, professor of Mechanical and Aeronautical Engineering at UC Davis and head of the Sports Biomechanics Laboratory. All teams stored their game balls in humidors this season, per Major League mandate. “It was introduced as a need in Colorado and then caught on.”

The Windup

Hubbard was referring to Denver’s Coors Field, once considered a baseball sideshow. Purists cringed as home run totals in the dry, thin air ballooned as alarmingly as Barry Bonds’s head. Balls travel nine percent further in the thin air (which is 18 percent less dense than in Boston), and become bouncier if left to harden in the desert climate. The end result made Coors Field baseball’s highest-scoring park, where seasons played out like a tragicomedy: “Pitchers gone wild.” 

Chicks dig the long ball, but nobody likes a loser. Colorado needed some gumption and they got it in spades from a Coors Field engineer who noticed how dry and shrunken his leather boots were after a duck hunt. Leather boots… cowhide balls…eureka! The thin air was beyond their control but its effect on baseballs was not.    

And look at them now—from laughing stock to World Series contenders. When Rockies General Manager Dan O’Dowd introduced the humidor in 2002, Coors Field mutated from the greatest hitter’s park of all time into one of baseball’s stingiest pitcher’s parks. Runs per game steadily dropped from 13.4 in 2001 to 10.6 in 2007; home runs per game dropped from 3.3 to 2.2. The humidor brought pitching—and wins—back to the Rockies.

The Pitch          

Pitching is both art and science. Successful hurlers get baseballs to dance past hitters’ bats by applying spin to the cowhide orbs. But that task is absurdly more difficult in Coors. First, Denver’s thin air reduces a baseball’s lift coefficient by 66 percent. The lift coefficient comprises air density, ball shape, orientation of spin and delivery point. Basically, balls move straighter one mile high, making them more hittable. Second, a thrower’s grip is diminished as dry air slicks, hardens, and slightly miniaturizes baseballs until they resemble “cue balls,” as pitcher Shawn Chacon once told ESPN. 

Simply put, Coors scrambles the lift coefficient—and with it, a pitcher’s confidence. Baseballs curve 50 percent more when thrown with all four seams spinning along the axis of rotation, said Hubbard. But baseball seams can sink into a dried-out ball, attenuating both grip and movement—an ill omen for pitchers. Take away a pitcher’s feel and ball movement, and he’s already half-beaten. Just ask Mike Hampton, whose sinker’s refusal to sink made his $120 million contract another Colorado punch line.

Hit hard!

A ball’s bounciness—or coefficient of restitution—plays the third key role in determining hitter/pitcher advantage. Humidity levels can either juice a ball or make it “dead inside,” said Robert Addair, Yale Sterling Professor of Physics and author of “The Physics of Baseball.” 

“We stored baseballs at 100% humidity for one month and found that the dead balls went 350 feet where the other balls went 400 feet,” said Addair. 

Dried-out baseballs perform more like bouncy super-balls. The coefficient of restitution’s “trampoline effect” increases, making Coors balls less “sticky” during the bat-to-ball collision. Conversely, waterlogged balls have all the zip of a sponge. The humidor should thus encourage home runs in damp places like Florida and Atlanta, while discouraging them in the Arizona desert, said Addair.

But foul?

But some are crying “foul ball!” over the humidor’s potential for abuse. Third baseman Jeff Cirillo once told ESPN that Coors balls were “heavy,” “spongy,” and “oblong,” implying Colorado was cranking up the humidity to deaden balls thrown to opponents.

While he’s since mellowed his stance, Cirillo’s comments do have precedent.  In 1965, Chicago White Sox groundskeeper Gene Broussard stored his team’s lively baseballs in one room while deadening his opponents’ balls in another room outfitted with a humidifier. And Dr. Addair recalled legendary manager John McGraw, who used a deep freezer for similar effects in the 1920’s. However, Milwaukee manager Ned Yost called Cirillo’s allegations “nuts” since both teams use the same balls in the modern game.

Tough pitch!

Be it humidor or better pitching, something went right at Coors. Sure, Boston swept them in the World Series, but it might have been for the best. Just reaching the postseason strained possibility; beating the Red Sox might have broken certain laws of the universe better left intact. 

Had Colorado actually won, would Isaac Newton have deserved a ring? Probably not. While America’s pastime is historically no stranger to Newton’s Laws, don’t expect ballparks to be confused with physics laboratories anytime soon—even as humidors standardize baseballs’ behavior.

“You can know that this angle and spin improves this and that coefficient,” said Hubbard. “But applying physics in a game that moves at 100 mph is pretty difficult.”