"Remember, a wooden bat is a 100 percent natural product," says Bill Williams of Hillerich & Bradsby, makers of the Louisville Slugger bats used by Major League Baseball. The bat makers evaluate the wood from the exterior, but they cannot look inside the bat for minute structural flaws.
Hillerich & Bradsby inspects each piece of wood in the form of a 40-inch-long, 3-inch-diameter piece called a billet. "The best grade goes into the professional bats," Williams says. Those are billets with straight, evenly spaced grain, with no pin knots or knotholes, and a consistent color with no dark spots. Despite these indications, it's possible that an inferior billet may pass muster because its flaws are not detectable from its exterior.
But sometimes even a good piece of wood will snap. Bats usually break in the handle area, where the diameter is smallest. Take a look at stop-action photography of a batter swinging and you'll be able to see that a wooden bat actually bends and bows during the swing, then snaps back into place.
Baseball players today typically grow up on thin-handled, lightweight, big-barreled aluminum bats, Williams points out. "Consequently, when they get to the pros, they like thin-handled, big-barreled wood bats."
"Most of the weight is situated in the barrel on a wooden bat, whereas it is more evenly distributed in an aluminum bat. Now you combine a big barrel with a thin handle with a 90-mph fastball, and a hitter who has been training with weights, and you set up the possibility of a broken bat."
A pitcher may also try to "saw the bat off" in the batter's hands, purposely throwing pitches inside to make the batter hit the ball on the thin handle and break the bat. A bat is also more likely to break in cold weather, when the wood is dryer and more brittle.
When a bat breaks, "most players blame the wood," says Williams. "They will say that Louisville Slugger just isn't buying the good wood like they used to. Well, the trees are usually 60 years old when we cut them down. And we have not changed our method of cutting and grading in more than a hundred years. While you can get a piece of wood that's a 'lemon,' most of the breakage is a result of contacting the ball on a wrong part of the bat."