It’s been a year-plus of speculation, increased home runs, and denials by the league and the commissioner, but it now looks as if there’s actual proof that baseballs have actually changed in recent seasons leading to the offensive spike.
FiveThirtyEight’s Rob Arthur, who along with The Ringer’s Ben Lindbergh has led the way with juiced ball research, tweeted on Wednesday “There’s now evidence that every part of the baseball has changed: core, yarn, and surface. I’m looking forward to that report from MLB’s task force.” Arthur’s report with the proof of this hasn’t published just yet, but Arthur’s commitment to this study is enough to think he has something concrete here.
In 2016 Arthur and Lindbergh published a piece dismissing many of the hypotheses floating around as explanations for the increase in dingers throughout the league. They tested two batches of balls — one from the Selig era and one from the Manfred era — but at that point they couldn’t accurately confirm there was a large enough variation in the ball to explain what was happening with the home run rate by that testing alone. By comparing statistics from Minor League and Major League games they came close though.
A year later the league supplied Lindbergh with an 11-page report insisting they had thoroughly tested the balls and that nothing was amiss, and then he published his own detailed report shortly after, coauthored with sabermetrician Mitchel Lichtman. In that report, they detailed the results of a test on the balls that Lichtman had done on his own and found that newer baseballs had “higher CORs and lower circumferences and seam heights” which seemed to amount for the dinger uptick. In that piece he also pointed out the huge amount of leeway the league has for its ball specifications, which would come into play in their later denials about ball changes.
Shortly after Arthur published more of his own research, this time using the sport’s camera and radar technology to “measure the speed of the ball shortly after the pitcher releases it and then again when it crosses the plate” and then “examining how much speed it loses between those two locations” to calculate air resistance. The data confirmed that drag on balls was lower in recent seasons and could account for up to 30 percent of the difference in home run rates.
A few weeks after that at the 2017 Home Run Derby, Manfred once again denied that anything was happening with the balls. He doubled down and said the league had never even discussed doing such a thing, nonetheless moved forward with juicing the balls intentionally.
During the playoffs, as players continued to voice their suspicions that the balls were indeed juiced, Manfred denied it again by saying,
“I’m absolutely confident that the balls that we’re using are within our established specifications. I think making a judgment based on seeing home runs in a single game just doesn’t make a lot of sense to me.”
“A single game”? Talk about missing the point as by that time it was way beyond focusing on the home runs in single games. After the World Series had wrapped, it was revealed at the GM meetings the league was once again investigating whether anything had changed with the balls and what affect that may have on the game.
Arthur then released a piece that included further research conducted by Keck School of Medicine at the University of Southern California and Kent State University’s Department of Chemistry and Biochemistry, which revealed the balls’ core, chemical composition, density. and volume had changed. That research involved x-raying the balls so they could study changes without destroying the balls first, which is super cool in addition to being a more effective way to look at a cross-section of balls from various seasons.
Earlier this year, the league instructed all teams to keep balls in climate-controlled rooms to further limit any variations even though they continue to insist everything falls within an acceptable range according to league specifications.
Arthur’s latest tweet doesn’t go into the details of how he’s confirmed the changes are concrete, but based on the work he and Lindbergh have done over multiple years he probably wouldn’t be claiming this if there weren’t some real evidence coming down the pike. We’ll update this post when Arthur releases his latest reporting on the topic. Until then, let’s operate under the assumption that the balls are indeed “juiced.”