Game changer: new rules limit the performance of baseball bats

In March 2010, Gunnar Sandberg, 16, was pitching for his team at Marin Catholic High School in Kentfield, Calif, when he threw a pitch that would change his life. The line drive came back at him traveling more than 160 kilometers (100 miles) per hour, striking his head and fracturing his skull. He spent the next three weeks in a coma, clinging to life.

Catastrophic injuries such as Gunnar’s are rare in baseball, but they are less rare than you might think. Baseball has the highest fatality rate of any sport among players ages 5 to 14, with an average of about four deaths each year. Even when injuries aren’t fatal, the consequences can be serious and lasting. Although Gunnar has largely recovered from his accident, he still suffers from seizures and memory loss.

The line drive that nearly killed Gunnar was struck using a metal bat. Soon after the accident, Gunnar’s school announced that it would switch to wooden bats. Traditional wooden bats are used by professional baseball players, but metal bats are the norm for just about everyone else, including most school leagues.

Are wooden bats safer than metal bats? Statistics are murky on that question, but many lab tests have demonstrated that baseballs struck by metal bats can and do travel faster and farther. A “hot” metal bat might smack a ball as much as 13 kilometers (8 miles) per hour faster and more than 15 meters (50 feet) farther than a wooden bat could- enough to turn an out into a home run.

COLLISION FORCE

A traditional wooden bat is constructed of one solid piece of ash or maple. Those hardwoods can withstand the extreme forces involved in a solid collision with a baseball-up to 8,000 pounds of force, equivalent to the weight of three cars. Metal bats are typically made of strong, lightweight aluminum, with a solid handle but a hollow barrel.

Even though a wooden bat and a metal bat may weigh the same, the metal bat will feel lighter and be easier to swing. Baseball players call that feeling the swing weight. It depends on a bat’s moment of inertia, a measure of how difficult it is to rotate something. Because the barrel of a metal bat is hollow, more of the bat’s weight is concentrated in the handle. That makes a metal bat easier to swing faster. As any seasoned player will tell you, faster swings make for harder, faster hits.

BOUNCE PER OUNCE

The bigger advantage of metal bats over wooden bats is something called the trampoline effect. It causes baseballs to spring off metal bats as if from a trampoline.

When a 145-kilometer- (90-mile-) per-hour pitch collides with a solid wooden bat, the baseball deforms incredibly, squashing to as little as half of its diameter before rebounding off the bat. In the process, a lot of precious kinetic energy, the energy of motion, is lost.

When the same pitch collides with a metal bat, the hollow barrel of the bat deforms, too, much as an empty foam cup does when you squash it sideways. The squashed bat stores the kinetic energy of the collision much more efficiently than the ball can. As the squashed bat unsquashes, the stored energy is released, sending the ball flying, as if from a trampoline.

High-performance metal bats are specially designed to exploit the trampoline effect. Composite nsa softball bats, for example, are aluminum bats that have a thin layer of graphite lining the wall of the barrel. That layer is stronger and lighter than aluminum and is designed to flex, amplifying the trampoline effect and increasing the speed of batted balls.

CRACKDOWN

New bat regulations have been adopted to rein in the trampoline effect of metal and composite bats. Those regulations will force the bats to perform more like wooden bats. The current standard for bats-called the ball exit speed ratio-is measured by comparing the speed of a baseball before and after it hits a particular bat. Starting next year, all bats used in high school games across the country must meet a tougher standard called the ball-bat coefficient of restitution (BBCOR). It’s a measure of the “bounciness” of the ball-bat collision.

BBCOR-approved bats became required equipment in college games this year, with dramatic results. Baiting averages are down by more than 20 points, and the number of home runs per game is off by 45 percent.

Doug MacLean, a coach at Marin Catholic, thinks the new BBCOR bats will do more than improve safety by slowing down batted-ball speeds. He expects that wooden and BBCOR bats will bring strategy back into the game. They’ll de-emphasize what’s called gorilla ball-power hitting and home runs-and put more stress on “small ball”-runs pieced together from base hits.

“Kids are going to be much better players,” says MacLean. “Before, you’d be down 3 to nothing in the fifth inning and you wouldn’t even be nervous. You knew one of your big kids was going to come up with a composite bat and clear the bases, and you’d be ahead 4 to 3. That doesn’t happen anymore. Now instead you’ve got to use your noggin.”

Feeling the Squeeze

When a baseball hits a bat, some of the ball’s kinetic energy (energy of motion) becomes potential energy (stored energy) for a split second, and some of it is lost. The potential energy then reverts to kinetic energy, shooting the ball into the field. A bat made of metal or a composite material absorbs more of the kinetic energy as potential energy than a wooden bat does. It becomes slightly squashed in the process. The greater the potential energy, the faster and farther the ball rebounds.

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