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.