Arthur: In MLB’s new home run era, it’s the baseballs that are juiced

From SABR member Rob Arthur at FiveThirtyEight on June 28, 2017:

Whether it’s witnessing the towering moonshots of Aaron Judge or Scooter Gennett’s four-homer game, every baseball fan has had a moment of home run shock this season. In the span of a few short years, MLB has gone from the age of the pitcher to the era of the dinger, and the evidence for why the shift occurred keeps pointing back to the baseball.

The baseball itself was initially identified as the most likely culprit for the spike in homers through a process of elimination. Ben Lindbergh and I documented the home run surge in detail last year, testing every hypothesis for its cause, including weather, performance-enhancing drugs, and the fly ball revolution. Each theory was rejected, leaving a solid trail of statistics that only a change in the ball would seem to explain. But identifying any alterations in the baseball becomes a problem of sample size. Without having a crate of game-used balls from each month of the season since July 2015, it’s difficult to find a concrete answer to baseball’s juiced-ball mystery.

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Originally published: June 29, 2017. Last Updated: June 29, 2017.