The cores of the baseballs used since 2015 have changed

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Last year two different studies — one by Ben Lindbergh and Mitchel Lichtman for The Ringer, and another by FiveThirtyEight’s Rob Arthur — found evidence that baseballs were altered at some point around the middle of the 2015 season. In 2015, 4,909 home runs were hit across the league. That wasn’t an alarming number. However, in 2016, 5,610 homers were hit, which was then the second-highest total of all time, trailing only 5,693 in 2000. In 2017, 6,105 home runs were hit, vastly eclipsing 2000’s all-time record.

The upshot of those studies was that the outside of the ball had changed to increase bounciness, to lower the seams and thus to reduce wind resistance, which could increase the distance a ball could fly. Today Arthur and Tim Dix of FiveThirtyEight have a new report about baseballs which show that something inside the ball has changed too: the core. The core of the balls used since the 2015 All-Star break — when homers suddenly and simultaneously spiked around baseball — is less dense than the core used before, which could add additional distance onto the flight of balls.

The upshot:

Combine all these factors together — a lighter, more compact baseball with tighter seams and more bounce — and the ball could fly as much as 8.6 feet farther. According to Nathan’s calculations, this would lead to a more than 25 percent increase in the number of home runs. Asked whether these changes in combination could have significantly affected the home run rate, MLB declined to comment.

Arthur and Dix note that homers have increased 46% since 2014 and suggest that the changed ball could account for over half of that, while uppercut swing strategies recently adopted by hitters could account for the rest.

Major League Baseball continues to be cagey about all of this, declining comment on these sorts of stories and offering disingenuous excuses for increased homers in order to avoid blaming the ball. The league is reportedly now studying the matter itself and is supposed to issue some sort of report about it all at some point.

If the league’s report does not deal with the above-mentioned studies and observations head-on and, instead, reads like a position paper denying such claims without providing underlying evidence and testing methodologies, it should be dismissed out of hand.