Major-league mystery.

As batters knocked ball after ball out of stadiums early this season, players and fans were left wondering: Is the baseball "juiced"?

Batter up, baseball sleuths. In the opening month of this year's baseball season, major leaguers belted 210 more home runs than they did last April. Are hitters just lucky or is something else driving balls out of the park?

Some players and managers claim that Rawlings Sporting Goods Co., the company that makes major league baseballs, "juiced up" the ball--changed it in some way so that it would bounce off the bat with more energy.

FOUL BALL?

"I wasn't convinced earlier, but I am now," said Detroit Tigers manager Sparky Anderson, after witnessing players not known for their homers start sending balls into the seats. "Soon [Rawlings is] going to have to make a statement that they souped up the ball," he says.

To get to the bottom of the homerun mystery, Science World decided to ask the folks at Rawlings what they'd done to the balls.

Rawlings spokesperson Scott Smith has a quick answer: Nothing at all. Ever since the company became the official baseball supplier for the major leagues in 1977, he says, they've been making baseballs exactly the same way, using exactly the same materials (see diagram, p. 14).

Sticking to major-league regulations, Rawlings workers weigh the balls, making sure each tips the scales at 5 to 5.25 ounces. In addition, they measure each ball's circumference, which must fall between 9 and 9.25 inches around. Finally, they test a sample of balls from each batch to make sure they all have the same "hitability."

To simulate hitting conditions, says Smith, "we fire the balls out of an air cannon [at 58 mph] against a northern white-ash wooden wall, which is the same material that baseball bats are made of." Their objective: Measure how much energy the balls retain when they bounce off the wall.

ENERGY DROP

Sailing through the air, a test ball has lots of kinetic energy, the energy of motion--just like an incoming pitch. In a fraction of a second, the ball smacks against the wood, compressing to three-quarters its diameter. Then, like a spring, the ball bounces back to its original shape and pushes off.

But the rebounding ball has less kinetic energy than it did before it hit the wall. That's because the collision produces lots of friction as the ball is squeezed on impact. The friction converts some of the ball's kinetic energy to another form of energy: heat.

To find out exactly how much energy a ball "loses," Rawlings workers measure its speed as it rebounds off the wall. Balls that make it to the majors must rebound at 30 to 34 mph, Smith says.

A "juiced-up" ball with, say, yams wound more tightly around its cork and rubber core, would rebound at a faster speed. A batter wouldn't have to swing as hard to knock one of these balls out of the park. But Rawlings maintains that the company rejects any balls with extra bounce, or "juice."

A DIFFERENT BALL GAME

To check up on Rawlings, Richard Larsen, a physicist at Brookhaven National Laboratory, conducted his own tests. He compared 1994 balls with a couple of major-league balls from 1987.

"We took the baseballs and we bounced them from 24 feet [off the ground]," Larsen says. "We dropped them onto concrete, and measured how much they bounced."

His conclusion: "The ball today doesn't bounce any more than the ball from 1987."

So if the balls haven't changed, what caused the sky-rocketing run of home runs? Most likely, something a lot less sinister than juiced balls.

Experts say the following variables deserve consideration: * More teams/poor pitching

In 1993, two new teams, the Florida Marlins and the Colorado Rockies, joined the majors. "Whenever you expand [the league], you decrease the quality of pitching," says Elrod Hendricks, a Baltimore Orioles coach. With the best pitchers spread over more teams and other less-skilled pitchers joining the majors, batters have a better shot at hitting over the fence. * Smaller strike zone

After watching instant replays of this year's home runs, Texas Rangers pitching coach Claude Osteen noticed that many homerun pitches were "giveaways"--easy-to-hit fastballs thrown right down the middle of the plate. With umpires calling more and more pitches "balls" (outside the strike zone), pitchers are forced to throw right over the plate to get strikes, he says. Such direct pitches are easier to knock out of the park. * Better training

Hitters deserve some credit for the home-run jump, says Baltimore Orioles outfielder and first baseman Jack Voigt. "From a physical standpoint, guys are just getting bigger, and stronger, and quicker," he says. In addition, each team now has extensive video libraries where players can watch any pitcher and see how he works hitters. That helps the batters know what to expect.

Will the trend toward more and more homers continue until each player routinely hits 60 to 70 per season? Will Rawlings eventually have to modify the ball to help pitchers?

That's not likely. Experts say hitting a baseball, not to mention hitting a home run, is still one of the most difficult things to do in sports. Even the best players get hits only 35 percent of the time. To knock one over the fence, says the Orioles' Voigt, "you have to hit the ball right on the nose."

Even last April, that only happened about one out of every 30 times a batter came to the plate.