Looking inside the balls and testing their chemical composition revealed that the cores of recent balls were somewhat less dense than the cores of balls used before the 2015 All-Star Game. The newer cores weigh about a half a gram less than the older ones, which might be enough to cause baseballs hit on a typical home run trajectory to fly about 6 inches farther. That alone is hardly enough to explain the home run surge of recent seasons, but when combined with previous research finding that baseballs began to change in other small ways starting around the same time, it suggests that a number of minor differences may have combined to contribute to the remarkable upswing in home run power we’ve witnessed since 2015.

Works which reference this piece

Following numerous studies, an MLB commission has confirmed that the baseball has changed since mid-2015.

How has the baseball evolved over two centuries? Moderately, but notably enough to change outcomes.

MLB has its own spin on the "positionless" trends found in other sports.

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What does it mean for the rest of the season?

After taking apart and examining twenty-six baseballs, a possible explanation for the rise in both home runs and pitcher blisters emerged: The laces in the newer baseballs are noticeably different.

Following numerous studies, an MLB commission has confirmed that the baseball has changed since mid-2015.