Mike Teevan, a spokesman for Major League Baseball, said the league does “extensive reviews of the performance of the baseball, and there have been no differences” to explain the increase in homers. Strikeouts, said starter Jon Lester of the Chicago Cubs, are also rising, and hitters are taking a different approach.

“I know our hitting coach wants you to hit the ball in the air,” Lester said. “There’s no slug on the ground. Guys are willing to take their punch-outs to hit the ball in the air, and swing hard in case they hit it.”

That theory would seem to make sense, especially as hitters react to the increasing use of extreme infield shifts. Yet the overall percentage of fly balls has not risen. According to Fangraphs, it is 34.2 percent now; only two of the past 15 seasons have been lower.

What has changed is that a greater percentage of fly balls are turning into home runs. At 12.9 percent, that figure is the highest it has been since Fangraphs started tracking the statistic in 2002. At least in one sense, perhaps, throwing harder may be working against pitchers.

“Secondary stuff isn’t as big of a thing as it used to be, I feel like,” Baltimore Orioles catcher Matt Wieters said. “It’s now, ‘Can you throw 98, 99?’ And a lot of breaking balls that are hanging end up getting hit out.

“That’s my theory: The types of arms that are getting moved through the system are guys that can really throw hard, and command sometimes comes later for them. But they get to the big league level while they’re throwing hard, and then they learn command. Home runs, more times than not, are mistakes — they’re not the wrong pitch, they’re just mistakes in the middle of the plate.”