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Baseball players are socking dingers at a truly historic rate, and everyone is wondering what the heck is going on. Through research and testing done by The Ringer and FiveThirtyEight and others, a convincing theory has emerged: the ball is juiced.


The juiced ball theory explains the rise in home runs by concluding that some time after the 2015 All-Star break, MLB started using baseballs that were constructed in a way to make them bouncier and thus more likely to travel farther off the bat. The league attempted to throw cold water on this theory by conducting its own internal test of the balls, which concluded that there was no difference between the balls that were used before and after the 2015 All-Star break.

However! The Ringer’s Ben Lindbergh commissioned his own independent study, and concluded that the newer balls are in fact juiced:

The newer balls have higher CORs [coefficient of restitution, or “bounciness”] and lower circumferences and seam heights, which would be estimated to add an average of 7.1 feet to their distance, equivalent to the effect we would expect to stem from a 1.43 mph difference in exit speed. Although those differences don’t sound enormous, Nathan has noted that “a tiny change in exit speed can lead to much larger changes in the number of home runs.” Last July, he calculated that an exit-speed increase of 1.5 mph would be sufficient to explain the rise in home runs to that point, which means that the 1.43 mph effective difference that Lichtman’s analysis uncovered could comport almost exactly with the initial increase in home runs. Lichtman calculates that a COR increase of this size, in this sample, falls 2.6 standard deviations from the mean, which means that it’s extremely unlikely to have happened by chance.

FiveThirtyEight’s Rob Arthur followed up on Lindbergh’s piece by using baseball’s own ball-tracking technology to measure changes in the ball’s drag coefficient. He concluded that, yes, the newer balls are having a much easier time soaring through the air:

Graphic via FiveThirtyEight

All of this would lead a reasonable person to conclude that the ball has been altered in a way that makes home runs more common. And that’s fine! Dingers are cool as hell and if the league wants more dingers, nobody is going to be too upset about it. And yet, commissioner Rob Manfred insists this isn’t the case. During an interview with Chris Russo at the Home Run Derby last night, Manfred said there’s no evidence that the ball is juiced:


The conversation continued, and Manfred said that juicing the ball has never even been discussed as an option by the league:

In the entire time I’ve been going to owners meetings, which dates back to 1988, not only has baseball never purposely altered the baseballs, I have never heard a conversation in which people have suggested we should purposely alter the baseball.


Rob, I don’t believe you.

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