Chicago Cubs slugger Sammy Sosa is in hot water for using a corked bat in last night's game versus Tampa Bay. How does corking a bat help a hitter?
Corking a bat lightens the lumber, which in turn increases bat speed and, the conventional wisdom holds, hit distance. Corkers typically drill a hole at the end of the bat, hollow out the "sweet spot," and fill it with wine corks or Superballs. The hole is then sealed with a combination of sawdust and pine tar. The result is a bat that's several ounces lighter than advertised, though still as long and thick as its heavier peers. A lighter bat, of course, is easier to whip through the strike zone.
The theoretical edge seems infinitesimal. Assume a corker reduces his bat's weight by 1.5 ounces. An average major league pitch travels from the pitcher's hand to the plate in a hair under half a second. The corked bat will give the hitter an additional five-thousandths of a second to see the pitch, judge it, and get the bat head moving through the strike zone.
A quicker bat may help a struggling hitter catch up with pitches, but it actually reduces his ability to smack long drives. The primary equation that determines a batted ball's distance is p = mv, where "p" is momentum, "m" is mass, and "v" is velocity. Though a corked bat will travel at a greater velocity, the tail-off in weight lessens the mass. As a result, sluggers like Sosa will actually see the length of their moon shots decrease. In his book The Physics of Baseball, Yale physicist Robert K. Adair estimated that a corked bat will shave about a yard off a 400-foot tater.
More likely to benefit, then, are slap hitters who specialize in singles. But the advantage is more psychological than anything else—a corked bat is essentially a placebo for hitters on the skids. They also splinter more readily, which makes catching the cheaters a lot easier. Rather than risk long suspensions, Adair advises, players should opt for lighter bats, perhaps by using a lighter grain of wood. Or they can just choke up three-quarters of an inch, which produces the same uptick in bat speed as corking.
Bonus Explainer: Surprisingly, the same major league baseball rules that outlaw corking make no mention of minimum or maximum bat weights, although there's a maximum length of 42 inches and a maximum diameter of 2.75 inches. The earliest set of codified rules for professionals, published in 1857, recommended bats that weighed up to 48 ounces. Today, given the abundance of pitchers who throw 95-mph cheese, players prefer much lighter bats; the current average weight is about 33 ounces.