A Staff Report from the Straight Dope Science Advisory Board

When do baseballs get taken out of play?

January 1, 2008

Dear Straight Dope:

A baseball must take a pretty stiff beating, being thrown somewhere around 90 mph and hit with great force by a swung bat. How is the ball made to withstand such blows? Obviously if the ball is hit into the stands or out of the park, it must be replaced, but it seems to me that the life span of a ball would be limited anyway. On average, how often does the umpire replace a baseball in play in a typical major league game? There are doubtless rules about when and/or how often the ball in play is to be changed. What are the guidelines?

SDStaff Gfactor replies:

As one might guess, the rules of baseball are pretty specific about what constitutes a regulation ball:

1.09 The ball shall be a sphere formed by yarn wound around a small core of cork, rubber or similar material, covered with two stripes of white horsehide or cowhide, tightly stitched together. It shall weigh not less than five nor more than 5 1/4 ounces avoirdupois and measure not less than nine nor more than 9 1/4 inches in circumference.

According to the Baseball Almanac Web site, these size and weight parameters have been around since before the inception of the National League in 1876. The cork center showed up in 1911, followed immediately by a surge in batting averages and runs scored; by 1931 the cork was encased in thin layers of rubber, which may or may not have deadened the ball a bit. (Raised seams, added at the same time, made it easier to throw breaking pitches.) All major league balls were covered in horsehide until this got too expensive; cowhide became the official covering after 1974.

On the question of how often the ball gets changed, the rules actually give the home plate umpire a fair amount of discretion. Per rule 3.01 (c)-(e), he's required to keep a supply of alternate baseballs on hand, to be introduced into play when the game ball leaves the field (as either a foul ball or a home run), when the pitcher requests a new ball, or when the ball in play "has become discolored or unfit for use." What this means in current practice, most estimates agree, is that the average baseball gets used for only about six or seven pitches before it's out of the game one way or another. Since a typical major league game takes roughly 290 pitches to complete these days, the home plate umpire might wind up replacing the ball nearly four dozen times.

The baseball analyst and historian Bill James has argued that the emphasis on removing "discolored or unfit" balls from use played an important role in the transition, circa 1920, from the so-called dead-ball era, when scoring was relatively low and the home run was a minor part of the game, to the lively-ball era that's essentially continued through the present. Up till then, umpires tended to leave the same ball in play if they could – fans were pressured to give back foul balls – and pitchers and fielders tended to deface the ball every chance they got. Balls were scuffed, scratched, and spat on to make them spin funny, and soiled to make them harder for the batter to see. Though the spitball was partially banned in late 1919, the real turning point came in August 1920 when star shortstop Ray Chapman of the Cleveland Indians was struck and killed by a pitch – reportedly not a spitball but just a fairly dirty ball he didn't seem to see well. "From then on," James writes, "much more effort was made to keep a clean, fresh ball in play."

Right around the same time, Babe Ruth was dismantling the long-held conventional wisdom that trying to hit the ball out of the park would just result in a lot of long fly outs; others followed his lead, and soon a full-fledged explosion of offense was under way. National League president John Heydler accused ball manufacturers of making their product livelier (possibly by winding the yarn tighter), but the manufacturers denied it; anyway, it's likely that the use of fresher, more visible balls was a bigger factor in the 1920s batting boom.

Besides what's set out in the rules, baseball has provided its official ball supplier, Rawlings, with additional specifications for manufacture, but some recent studies have questioned whether these standards have been uniformly applied. In 2000 a team of University of Rhode Island scientists reported that the cores of major league baseballs from 1995 and 2000 bounce higher than ones from the 60s and 70s and that they contain materials that could make them livelier. But another study found no difference between balls manufactured in 1999 and 2000, despite a jump in the number of home runs in 2000. Of course, there are other possible reasons for an upswing in homers – as baseball fans have become all too aware in recent years.

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Staff Reports are written by the Straight Dope Science Advisory Board, Cecil's online auxiliary. Though the SDSAB does its best, these columns are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.

References

"Baseball's Dirty Side"

"Baseball Rule Change Timeline," Baseball-almanac.com

Bert, Ray, "Stepping Up To The Plate," ASEE Prism Online

A Cooperstown Tradition Since 1940: The Hall of Fame Game, Baseball Hall of Fame

Hall, Carl, "The Art and Science of 'Barry Ball'; Reflexes, Precise Eye Baffle Experts," San Francisco Chronicle, October 21, 2002

Ingraham, Jim, "Tools of the Trade," March 16, 2006

James, Bill, The New Bill James Historical Baseball Abstract, Free Press 2001

Johnson, Ted, The History of the Baseball, Fogdogsports.com

Kaat, Jim, "Baseball's New Baseball," Popular Mechanics, October, 2000

McPhee, Mike, "Game's Centerpiece Takes Lots of Work," Denver Post, July 6, 1998, A-01

Nathan, Alan, "The Physics of Baseball"

Schofield, Paul, "Mud a Mainstay in America's Pastime," Pittsburgh Tribune-Review, July 17, 2005

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