X-ray of baseballs reveals possible cause of home run surge

The home run surge of 2017 (and before) has been a heck of a lot of fun, but there are many outstanding questions about what’s really behind it. And now we might have the most compelling answer yet. Rob Arthur and Tim Dix of FiveThirtyEight published the findings of CT scans and other experiments that had been done on new and game used baseballs from before and after the official start of the surge (the 2015 All-Star Game), and what they’re reporting is undeniable: the core of the baseball has changed.

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Arthur and Dix reported the findings of experiments commissioned by ESPN Sports Science. A CT scan was done on eight different baseballs: one purchased new from Rawlings, four game-used balls from April 2014 through May 2015 (before the surge began), and three game-used balls from August 2016 through July 2017 (after the surge started). The CT scan revealed that the core of the newer baseballs are approximately 40% less dense than the older balls. Further testing of the chemical composition of the less dense baseballs revealed that Rawlings used a more porous substance to seal the core, which led to the decrease in density.

A less dense core means a lighter baseball, and the newer baseballs are an average of 0.5 grams lighter than the old ones. Arthur and Dix admit that a lighter baseball on its own wouldn’t cause a huge jump in homers. But when added to existing research on the new baseballs done by Arthur at FiveThirtyEight and Ben Lindbergh of The Ringer, it turns into something significant.

Combine all these factors together — a lighter, more compact baseball with tighter seams and more bounce — and the ball could fly as much as 8.6 feet farther.

What’s insane is that even the new home run friendly baseball doesn’t account for the entire home run spike. According to physicist Alan Nathan, all those changes together would only increase home runs by 25 percent. Since home runs increased by about 46 percent between 2014 and 2017, Arthur and Dix believe that a change in hitting philosophy is responsible for the other 21 percent. More players are focusing on launch angle and hitting the ball upward to increase their chance of getting the ball in the air, which increases the likelihood of hitting a home run.

Related: Look back at the slugfest that was the 2017 World Series: 

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The best photos from the 2017 World Series
LOS ANGELES, CA - OCTOBER 25: Logan Forsythe #11 of the Los Angeles Dodgers scores a run on a RBI single hit by Enrique Hernandez #14 (not pictured) to tie the game 5-5 during the tenth inning as Brian McCann #16 of the Houston Astros is unable to make the tag in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Sean M. Haffey/Getty Images)
LOS ANGELES, CA - OCTOBER 25: Yasiel Puig #66 of the Los Angeles Dodgers licks his bat during the seventh inning against the Houston Astros in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Christian Petersen/Getty Images)
LOS ANGELES, CA - OCTOBER 25: Joc Pederson #31 of the Los Angeles Dodgers celebrates after hitting a solo home run during the fifth inning against the Houston Astros in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Harry How/Getty Images)
Oct 28, 2017; Houston, TX, USA; Los Angeles Dodgers designated hitter Joc Pederson (31) hits a three-run home run against the Houston Astros in the 9th inning in game four of the 2017 World Series at Minute Maid Park. Mandatory Credit: Thomas B. Shea-USA TODAY Sports TPX IMAGES OF THE DAY
LOS ANGELES, CA - OCTOBER 24: Dallas Keuchel #60 of the Houston Astros throws a pitch during the first inning against the Los Angeles Dodgers in game one of the 2017 World Series at Dodger Stadium on October 24, 2017 in Los Angeles, California. (Photo by Tim Bradbury/Getty Images)
LOS ANGELES, CA - OCTOBER 25: Chris Taylor #3 of the Los Angeles Dodgers loses his hat as he attempts to catch a RBI single hit by Alex Bregman #2 of the Houston Astros (not pictured) during the third inning in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Ezra Shaw/Getty Images)
LOS ANGELES, CA - OCTOBER 25: Corey Seager #5 of the Los Angeles Dodgers celebrates after hitting a two-run home run during the sixth inning against the Houston Astros in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Christian Petersen/Getty Images)
LOS ANGELES, CA - OCTOBER 25: Marwin Gonzalez #9 of the Houston Astros runs the bases after hitting a solo home run during the ninth inning against the Los Angeles Dodgers in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Ezra Shaw/Getty Images)
LOS ANGELES, CA - OCTOBER 25: Carlos Correa #1 and Jose Altuve #27 of the Houston Astros celebrate after hitting solo home runs during the tenth inning against the Los Angeles Dodgers in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Harry How/Getty Images)
LOS ANGELES, CA - OCTOBER 25: Logan Forsythe #11 of the Los Angeles Dodgers scores a run on a RBI single hit by Enrique Hernandez #14 (not pictured) to tie the game 5-5 during the tenth inning against the Houston Astros in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Harry How/Getty Images)
LOS ANGELES, CA - OCTOBER 25: George Springer #4 of the Houston Astros celebrates in the dugout after hitting a two-run home run during the eleventh inning against the Los Angeles Dodgers in game two of the 2017 World Series at Dodger Stadium on October 25, 2017 in Los Angeles, California. (Photo by Harry How/Getty Images)
HOUSTON, TX - OCTOBER 27: Yuli Gurriel #10 of the Houston Astros hits a solo home run during the second inning against the Los Angeles Dodgers in game three of the 2017 World Series at Minute Maid Park on October 27, 2017 in Houston, Texas. (Photo by Ezra Shaw/Getty Images)
HOUSTON, TX - OCTOBER 27: Josh Reddick #22 of the Houston Astros slides in to home plate during the fifth inning against the Los Angeles Dodgers in game three of the 2017 World Series at Minute Maid Park on October 27, 2017 in Houston, Texas. (Photo by Bob Levey/Getty Images)
HOUSTON, TX - OCTOBER 27: Justin Turner #10 of the Los Angeles Dodgers scores on a wild pitch by Brad Peacock #41 of the Houston Astros during the sixth inning in game three of the 2017 World Series at Minute Maid Park on October 27, 2017 in Houston, Texas. (Photo by Ezra Shaw/Getty Images)
HOUSTON, TX - OCTOBER 28: Cody Bellinger #35 of the Los Angeles Dodgers reacts as he hits a RBI double during the ninth inning against the Houston Astros in game four of the 2017 World Series at Minute Maid Park on October 28, 2017 in Houston, Texas. (Photo by Tom Pennington/Getty Images)
HOUSTON, TX - OCTOBER 29: George Springer #4 of the Houston Astros dives and fails to make a catch on a RBI triple by Cody Bellinger #35 of the Los Angeles Dodgers (not pictured) during the seventh inning in game five of the 2017 World Series at Minute Maid Park on October 29, 2017 in Houston, Texas. (Photo by Christian Petersen/Getty Images)
HOUSTON, TX - OCTOBER 29: Cody Bellinger #35 of the Los Angeles Dodgers gestures after hitting a three-run home run during the fifth inning against the Houston Astros in game five of the 2017 World Series at Minute Maid Park on October 29, 2017 in Houston, Texas. (Photo by Jamie Squire/Getty Images)
Oct 29, 2017; Houston, TX, USA; Los Angeles Dodgers first baseman Cody Bellinger (35) climbs into the stands to catch a foul ball hit by Houston Astros shortstop Carlos Correa (not pictured) in the 9th inning in game five of the 2017 World Series at Minute Maid Park. Mandatory Credit: Matthew Emmons-USA TODAY Sports TPX IMAGES OF THE DAY
HOUSTON, TX - OCTOBER 30: Alex Bregman #2 of the Houston Astros hits a game-winning single during the tenth inning against Kenley Jansen #74 of the Los Angeles Dodgers in game five of the 2017 World Series at Minute Maid Park on October 30, 2017 in Houston, Texas. (Photo by Ezra Shaw/Getty Images)
HOUSTON, TX - OCTOBER 30: Alex Bregman #2 of the Houston Astros celebrates with teammates after hitting a game-winning single during the tenth inning against the Los Angeles Dodgers in game five of the 2017 World Series at Minute Maid Park on October 30, 2017 in Houston, Texas. The Astros defeated the Dodgers 13-12. (Photo by Jamie Squire/Getty Images)
HOUSTON, TX - OCTOBER 30: Derek Fisher #21 of the Houston Astros slides in to home plate scoring the game winning run during the tenth inning against Austin Barnes #15 of the Los Angeles Dodgers in game five of the 2017 World Series at Minute Maid Park on October 30, 2017 in Houston, Texas. The Astros defeated the Dodgers 13-12. (Photo by Tom Pennington/Getty Images)
Nov 1, 2017; Los Angeles, CA, USA; Houston Astros center fielder George Springer (4) celebrates with teammates Jose Altuve (27) , Alex Bregman (2) and Marwin Gonzalez (9) after hitting a two-run home run against the Los Angeles Dodgers in the second inning in game seven of the 2017 World Series at Dodger Stadium. Mandatory Credit: Jayne Kamin-Oncea-USA TODAY Sports TPX IMAGES OF THE DAY
Nov 1, 2017; Los Angeles, CA, USA; Houston Astros first baseman Yuli Gurriel (10) celebrates after forcing out Los Angeles Dodgers shortstop Corey Seager (5) in the 9th inning to win game seven of the 2017 World Series at Dodger Stadium. Mandatory Credit: Gary A. Vasquez-USA TODAY Sports TPX IMAGES OF THE DAY
Nov 1, 2017; Los Angeles, CA, USA; Houston Astros pitcher Charlie Morton (50) and catcher Brian McCann (16) celebrate with teammates after defeating the Los Angeles Dodgers in game seven of the 2017 World Series at Dodger Stadium. Mandatory Credit: Gary A. Vasquez-USA TODAY Sports TPX IMAGES OF THE DAY
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It will shock no one that MLB has nothing new to say about these findings. Commissioner Rob Manfred, who has consistently denied that anything significant has changed about the baseballs, formed a committee in November to investigate any changes to the baseball. The full results have yet to be released to the public, but what they found (or did not find) probably won’t surprise you.

According to Alan Nathan, one of the physicists on the commission, the task force found that all the characteristics that MLB regularly measures, including the weight, circumference, seam height and bounciness of the ball, were within ranges that meant variations in the baseballs were unlikely to significantly affect home run rates. MLB declined to provide the data supporting these assertions.

But Arthur and Dix have presented scientific evidence that directly refutes those unsupported findings. The core, as well as other aspects of the baseball, has changed. The biggest question now is whether Manfred has an explanation for that, or if he’ll even bother to recognize it at all.

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Liz Roscher is a writer for Yahoo Sports. Have a tip? Email her at lizroscher@yahoo.com or follow her on twitter! Follow @lizroscher

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