All across Mississippi’s baseball fields, the ping of aluminum is being replaced with the clunk of composite. Impressive home runs are turning into sharp, line drive singles and base hits to groundouts.

The reason, in simple terms, is the bats. In complicated terms, it’s something called “ball-bat coefficient of restitution” — BBCOR for short — which is a measurement of how fast the ball leaves the bat.

The Mississippi High School Activities Association has mandated the use of BBCOR bats beginning next season. Mississippi’s high school teams have started working with them this month during the summer schedule, and players and coaches alike say it will change the way the game is played.

Instead of relying on power, teams will be forced to focus on defense and pitching, Warren Central coach Josh Abraham said.

“All it’s really doing is leveling the playing field. The most fundamentally sound teams that bunt and pitch well will be the teams on top,” Abraham said. “It’s good for parity in the state. The teams that play gorilla ball, now they’ll have to focus on the finer points. It will just change the way coaches coach and prepare.”

The BBCOR bats were adopted by the NCAA for the 2011 season, and offensive production dropped almost immediately. Team batting averaged fell by almost 30 points from 2010 and scoring was down by more than one run per game.

The bats use composite materials, rather than the springy aluminum previous bats were made of. The composites slow the speed at which the ball leaves the bat and more closely resemble wood. To be certified as meeting the BBCOR specifications, bats are tested and must meet a mathematical standard.

The BBCOR bats also have a smaller sweet spot, where the ball makes its best contact. That makes it more difficult to drive a ball, players said.

“We’ve hit with them for four games. It’s a lot harder. They’re so much more top heavy that it’s hard to hit on the sweet spot,” said Matthew Foley, a sophomore infielder for St. Aloysius. “You’ve just got to quit trying to hit home runs and try to get base hits with them.”

Because it’s more difficult to crush a baseball with the new bats, how players approach hitting is likely to change. Learning exactly where to swing the bat and place the ball will become more valuable skills than being able to lift fly balls.

“It puts more focus on hitting with the sweet spot and how it’s supposed to be hit, instead of swinging for the fences,” said Sam Staggs, a senior first baseman at Porters Chapel Academy.

The BBCOR bats became widely available in the spring. Although some teams added them to the inventory, few used them during games because of the differences between the new and old bats.

“We swung the trampoline last season,” Staggs said with a laugh.

Taking away some of the offensive firepower isn’t all bad. St. Al, for example, will have a lineup full of underclassmen next season. As a team, it hit two home runs in 2011 and isn’t likely to hit many more in 2012.

The small ball style that’s expected to come with the new bats will suit their talent well.

Abraham said it will also help his Warren Central team. Although the Vikings have some pop in the lineup, they’re expected to rely more on pitching and defense next season — exactly what the BBCOR bats play to.

“It’s definitely shortened the game for us, and can definitely benefit us more than hurt us with the way we approach the game,” Abraham said. “It’s not going to change our philosophy.”