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10 Degrees: Is a juiced ball causing MLB's large home run spike?
It’s hitters and pitchers and coaches and executives and even rational, cogent analysts who cannot find a reasonable explanation for the spike in home runs dating back to last August. The HR/FB rate – the percentage of fly balls that end up over the fence – spiked over the season’s final two months, and it has continued this April.
With 11.8 percent of fly balls leaving the yard in the season’s first month, it marked the highest April rate since the league started tracking the data in 2002. The number mirrored those of August (12.2 percent) and September (12.3 percent), which Hardball Times analyst Jon Roegele noticed after not even a month. Roegele studied it and came to an impasse.
“I couldn't find anything to describe that amount of HR/offensive change, as far as weather, strike zone, where pitchers were pitching, etc.,” he wrote in an email this week. “I suspected that they changed something with the balls after the All-Star break last year as nothing else in the data could explain it.”
When the email landed, I thought I heard black helicopters whirling above. On the eve of the season, Ben Lindbergh and Rob Arthur at Five Thirty-Eight investigated the HR/FB spike and all the causes that leap to the mind’s forefront. They even sent balls from 2014 and 2015 to a lab for testing to see any differences. None showed. They might as well have been the same.
As much as that should have quelled my interest, the study only emboldened it. One month is one thing. Two months is another. Three is a trend, a pattern, something worth exploring, and with April home runs at their highest rate in more than a decade – 2.77 percent of plate appearances ended with a homer – it warranted a deeper dive.
So I touched base with Dr. Alan Nathan, a professor emeritus at the University of Illinois and the foremost expert on baseball physics. In trying to understand what happened last fall, Nathan had studied the new exit-velocity data from the league’s Statcast system. While the ball’s speed off the bat had increased ever so slightly in the last two months, Nathan wrote, “a 1 mph change in mean exit speed can account for essentially all of the 13% change in home runs.”
In other words, all it would take to inject offense into baseball is a tiny difference in how the ball leaves the bat. And that difference has continued into this season. Nathan looked at balls with between a 15- and 45-degree launch angle – the optimal trajectory for home run balls. He found nearly 150 more balls were hit this April between 104 and 112 mph compared to last year.
“The conclusion seems to be similar to the early season/late season comparison from 2015,” Nathan said in an email. “Namely, a small increase in exit speeds leads to a big increase in HR production.”
The question, now, is why balls are coming off the bat so much harder now.
“I won't speculate why there might be a small increase in exit speeds,” Nathan said.
Oh, come on, doc.
“It could happen for any number of reasons,” he said.
Like a juiced ball!
“It would appear that the increase in home runs is attributable to exit speeds,” Nathan said, “not atmospheric conditions.”
OK, so weather is out. Now, it’s possible players suddenly, collectively got stronger. Positive tests for performance-enhancing drugs, for example, have jumped this season – there were none last August or September, for whatever that's worth – though as Dee Gordon’s shows, the idea that PEDs exist to aid and abet only home run hitters is false. We can’t discount PEDs entirely, but no evidence exists that drug users – some of whom could use the substances for endurance rather than strength – hit the ball any harder than clean players. Nathan did argue in a paper that PED use would increase muscle mass, and muscle mass would make it likelier a ball go over the fence.
It’s probably not different, higher-quality wood, even as bat regulations have gotten more restrictive in recent years. And while it’s possible this amounts to little more than a big coincidence, three straight months – over two seasons no less – lessens that likelihood.
Like exit velocity, the tiniest changes in the ball can have significant effects, and as much as Major League Baseball focuses on quality control, the ball is the first guess in this game of Clue. A league spokesman said: “We tested the balls halfway through last season and confirmed there was no change in composition from the beginning of the season. We didn’t make any changes in the offseason, either.”
A-ha! In June and July 2015, around the halfway mark of the season, the home run rates were 10.6 and 11.1 percent respectively. And if the ball did change, it was after that, meaning … I’m grasping for straws.
It’s hitters and pitchers and coaches and executives and even rational, cogent analysts who cannot find a reasonable explanation for the spike in home runs dating back to last August. The HR/FB rate – the percentage of fly balls that end up over the fence – spiked over the season’s final two months, and it has continued this April.
With 11.8 percent of fly balls leaving the yard in the season’s first month, it marked the highest April rate since the league started tracking the data in 2002. The number mirrored those of August (12.2 percent) and September (12.3 percent), which Hardball Times analyst Jon Roegele noticed after not even a month. Roegele studied it and came to an impasse.
“I couldn't find anything to describe that amount of HR/offensive change, as far as weather, strike zone, where pitchers were pitching, etc.,” he wrote in an email this week. “I suspected that they changed something with the balls after the All-Star break last year as nothing else in the data could explain it.”
When the email landed, I thought I heard black helicopters whirling above. On the eve of the season, Ben Lindbergh and Rob Arthur at Five Thirty-Eight investigated the HR/FB spike and all the causes that leap to the mind’s forefront. They even sent balls from 2014 and 2015 to a lab for testing to see any differences. None showed. They might as well have been the same.
As much as that should have quelled my interest, the study only emboldened it. One month is one thing. Two months is another. Three is a trend, a pattern, something worth exploring, and with April home runs at their highest rate in more than a decade – 2.77 percent of plate appearances ended with a homer – it warranted a deeper dive.
So I touched base with Dr. Alan Nathan, a professor emeritus at the University of Illinois and the foremost expert on baseball physics. In trying to understand what happened last fall, Nathan had studied the new exit-velocity data from the league’s Statcast system. While the ball’s speed off the bat had increased ever so slightly in the last two months, Nathan wrote, “a 1 mph change in mean exit speed can account for essentially all of the 13% change in home runs.”
In other words, all it would take to inject offense into baseball is a tiny difference in how the ball leaves the bat. And that difference has continued into this season. Nathan looked at balls with between a 15- and 45-degree launch angle – the optimal trajectory for home run balls. He found nearly 150 more balls were hit this April between 104 and 112 mph compared to last year.
“The conclusion seems to be similar to the early season/late season comparison from 2015,” Nathan said in an email. “Namely, a small increase in exit speeds leads to a big increase in HR production.”
The question, now, is why balls are coming off the bat so much harder now.
“I won't speculate why there might be a small increase in exit speeds,” Nathan said.
Oh, come on, doc.
“It could happen for any number of reasons,” he said.
Like a juiced ball!
“It would appear that the increase in home runs is attributable to exit speeds,” Nathan said, “not atmospheric conditions.”
OK, so weather is out. Now, it’s possible players suddenly, collectively got stronger. Positive tests for performance-enhancing drugs, for example, have jumped this season – there were none last August or September, for whatever that's worth – though as Dee Gordon’s shows, the idea that PEDs exist to aid and abet only home run hitters is false. We can’t discount PEDs entirely, but no evidence exists that drug users – some of whom could use the substances for endurance rather than strength – hit the ball any harder than clean players. Nathan did argue in a paper that PED use would increase muscle mass, and muscle mass would make it likelier a ball go over the fence.
It’s probably not different, higher-quality wood, even as bat regulations have gotten more restrictive in recent years. And while it’s possible this amounts to little more than a big coincidence, three straight months – over two seasons no less – lessens that likelihood.
Like exit velocity, the tiniest changes in the ball can have significant effects, and as much as Major League Baseball focuses on quality control, the ball is the first guess in this game of Clue. A league spokesman said: “We tested the balls halfway through last season and confirmed there was no change in composition from the beginning of the season. We didn’t make any changes in the offseason, either.”
A-ha! In June and July 2015, around the halfway mark of the season, the home run rates were 10.6 and 11.1 percent respectively. And if the ball did change, it was after that, meaning … I’m grasping for straws.
