It's a good era for home runs, the current one. Last season, teams hit 1.26 home runs per game, which is an all-time record by a large margin. We've also seen a steep rise in recent years: 










That trend stands out even more when you consider that overall run scoring is down from the previous great home run era of the late 1990s/early 2000s. As such, home runs right now make up a larger proportion of run scoring than ever before. 

This home run boomlet has led fans, writers, and even players to wonder aloud whether the ball is juiced. Indeed, a study released in March found that baseballs in use after the 2015 All-Star break had less dense cores than their predecessors. MLB has pushed back against this notion in the past, and on Thursday they released the results of their own investigation into the matter and are considering five new steps from the research committee. Here's what you need to know about the results:

The committee consisted of outside experts

MLB didn't conduct this experiment itself. In August of 2017, commissioner Rob Manfred brought together various experts in the fields of physics and quantitative analysis to study the baseballs. The committee consisted of: 

  • Alan Nathan (Chairman) – Professor of Physics Emeritus, University of Illinois
  • Jim Albert – Professor of Statistics, Bowling Green State University
  • Jay Bartroff – Professor of Mathematics, University of Southern California
  • Roger Blandford – Professor of Physics, Stanford University
  • Dan Brooks – Owner of
  • Josh Derenski – Ph.D Student, Marshall School of Business, University of Southern California
  • Larry Goldstein – Professor of Mathematics, University of Southern California
  • Peko Hosoi – Professor of Mechanical Engineering, Massachusetts Institute of Technology
  • Gary Lorden – Professor Emeritus of Mathematics, California Institute of Technology
  • Lloyd Smith – Professor of Mechanical & Materials Engineering, Washington State University

The committee focused their efforts on studying the physical properties of the baseball, weather and climate conditions and player behavior. In addition to using StatCast data and conducting controlled experiments involving 180 unused official baseballs that date from 2013 to 2017, the committee also inspected Rawlings' production plant in Costa Rica. 

The investigation found no obvious changes to the baseball itself

To quote the committee's executive summary of its findings: 

Though there was a range in each measured parameter, in each case, both the new balls and authentication balls were consistently within specifications. In fact, for some of the tested parameters, such as weight, size, and COR, Rawlings achieved much greater precision than allowed by the MLB specifications. Any variation detected was relatively small on the practical scale, and there was no evidence that it could have produced an alteration in home run frequency on the order of the increase that has been observed. What's more, the annual trends of weight and circumference do not correlate with the home run increase.

The key finding is with regard to the COR, or coefficient of restitution, which is in essence the "bounciness" of the baseball. This investigation found it and other properties to be normal. A frequent criticism is that MLB's ball specifications are too wide-ranging and permissive. This study, though, found that, "Rawlings achieves far greater precision in COR than is communicated by that standard, and there is no evidence from the laboratory testing of baseballs-whether by Rawlings, UMass/Lowell, or the Sports Sciences Laboratory at Washington State University-that changes in the COR or CCOR (cylindrical coefficient of restitution)  of the ball has played a major contributing role in the home run surge."

So while, yes, MLB's specs are exacting enough, Rawlings went above and beyond. 

Player behavior doesn't appear to be a key factor

We're of course seeing many batters adjust their swings so as to afford a more optimal launch angle. It's all in an effort to hit the ball hard and in the air, and reconstructed sluggers like J.D. Martinez, Josh Donaldson, and Justin Turner prove it can work to great effect for certain batsmen. On another level, teams these days seem to be focusing more on players who can drive the ball, even at the expense of high contact rates. This team of scientists, though, didn't identify all of this as a cause of the home run surge. The key finding: 

The team found that exit velocities decreased slightly from 2016 to 2017, which would tend to lead to fewer, nor more, home runs. Launch angles exhibited a small increase, but only for the players with lesser home run talents. And spray angles were quite stable over the time period of the home run surge.

And that brings us to ... 

Something's going when the ball is in the air

It's not how the ball leaves the bat that's causing all this, at least according to this research. Rather, it's how the ball is behaving in the air that's leading to more home runs -- it's the aerodynamics. In 2014, for instance, home runs occurred on 9.5 percent of fly balls. Last season, that figure was up 13.7 percent, the highest on record. 

So what's happening? The committee found that rising temperatures were not the cause. Here's what they did find: 

The results of all these studies was that while changes in lift were not as apparent, the drag coefficient of Major League baseballs has decreased since 2015.

The drag coefficient is how the ball slows down on its path. More: 

To determine whether this change could feasibly account for the increase in home runs, the investigative team used a physics model to calculate that if the change in the home run rate from 2015 to 2017 were due entirely to changes in drag, one would expect the drag coefficient to have decreased by approximately 0.012. Both procedures performed-the experimental tests at WSU and the mathematical analysis of StatCast data-indicate that the drag coefficient has changed by approximately 0.0153 since 2015, an amount sufficient to have caused the home run surge.

This supports the conclusion that the reason for the surge in home runs is reduced drag on the baseballs, leading to better carry.

The increased carry they discovered is not, according to the report, correlated with changes in the size, weight, or seam height of the baseball. 

So what is it?

By the committee's own admission, they're in theoretical territory at the moment. Presently, they're testing to see whether this latest generation of baseballs is more symmetrical than baseballs past. Being something closer to a perfect sphere with a more balanced center of gravity would reduce drag, which, in turn, would increase carry. There's also the possibility of the baseball having a smoother surface these days, which would also reduce drag. 

Here's an important note in the study regarding those possible variations: 

There is also no evidence that any variations in the ball occur either intentionally or through substandard quality control by Rawlings. If anything, they would be inherent to the manufacturing process, which relies on substantial "by hand" labor.

The committee has recommendations 

What to do about all of this? The committee that Manfred assembled offers up these possible remedies and quality-control measures:

1. Monitoring of Temperature and Humidity Conditions. The Commissioner's Office is monitoring temperature and humidity in the ball storage locations of the 30 ballparks and will work with the committee on whether to require the use of humidors at all ballparks for the 2019 season.

2. Review of Production Specifications of Baseballs.  The Commissioner's Office is working with Rawlings to make updates to the existing production specifications of baseballs and to develop additional specifications for the aerodynamic properties of the ball.

3. Perform Aerodynamic Testing on Baseballs.  In addition to the existing testing protocol, the Commissioner's Office is working with the committee to develop a set of aerodynamic tests for game baseballs.

4. Create Standards for Mud Rubbing.  The Commissioner's Office is providing Clubs with guidance on the appropriate mud rubbing of baseballs, which will be enforced by the umpires.

5. Formation of a Scientific Advisory Council.  Some members of the committee will continue to advise the Commissioner's Office on issues related to baseball performance, as well as other science-related topics.

Via MLB's announcement, Manfred released the following statement: 

"I thank the committee for all of its hard work on this important issue.  Based on the results of their study, I am accepting their recommendations immediately and look forward to their continued guidance in this area."

On the other hand, people seem to like home runs, so the first step is deciding whether this is a problem worth solving.