What is causing the home run surge? A look into Baseball physics
Hopefully everyone is recovering well from the emotional hangover the Houston Astros gave us after suffering from the gentlemen sweep generated by a tough Boston Red Sox team. But the show must go on.
In 2017, Major League Baseball was on pace to have the highest rate of homeruns in its history. MLB was getting a lot of negative publicity. People were assuming that the balls were being altered, or ‘juiced’, in order to make them go further. In 2014, the rate of homeruns per team per game was 0.86, in 2015 it rose to 1.01, in 2016 the rate increased to 1.16, and in 2017 the homerun rate was 1.26. Many pitchers complained that the balls were noticeably bouncier, and even Alex Bregman spoke on the topic by humorously replying to a tweet from a suspicious Trevor Bauer, “Relax Tyler, those World Series balls spin different (crying Emoji).”
MLB called upon physics Professor Alan Nathan from the University of Illinois to form a committee of fellow scientists to figure out exactly why baseballs were traveling further. Even though most of us are pleased to see booming homers at ballparks across the country, there are still historical aspects that we as fans still appreciate. “A homerun hit today, should mean the same thing as a homerun that was hit 50 years ago. Records that were set back then shouldn’t be broken in the current environment because of changes either in the players (the other juicing scandal), or changes to the ball. I think MLB is sensitive to that, and I think fans are sensitive to that as well.”, claims Professor Nathan. The idea is to try and preserve the purity and historical significance of the sport.
The committee led by Professor Nathan had no ax to grind with MLB. The committee worked completely independent from the league and had their full cooperation by having access to StatCast data. The committee also used their own independent labs to test the various physical properties of the baseballs. They even had access to the Rawlings factory in Costa Rica to analyze if any differences existed throughout the years in the production of MLB used baseballs. Here’s what they found.
Two questions were asked to explain the sudden spike in homeruns.
The first question asks, is the surge in homeruns due to a change in the launch conditions of the ball coming off the bat? Which can come from a higher exit velocity of the baseball, causing longer fly balls. Basically, this is asking if balls are now bouncier than before at the point of contact with the bat, explained by the physics equation dubbed the Coefficient of Restitution. The answer is no, the Coefficient of Restitution has remained the same throughout the years. In fact, the committee found that Rawlings actually exceeds the expected requirements for the limitations of the bounciness in their baseballs.
The second question is, are players hitting at more optimum launch angles at a given exit velocity? This also causes the ball to travel further. Basically, this is asking if hitters are altering their swing mechanics to achieve greater launch angle revolutions post contact with the baseball, causing more homeruns. Red Sox slugger, JD Martinez, is a prime example of this change in swing mechanics after altering his swing on the advice of his hitting coaches in SoCal. Interestingly, he was with the Astros during this transformation and was actually referred there by another former Astro, Jason Castro. The answer for this question is also no, optimum launch angles at given velocities are not seen as a collective effect big enough to increase the yearly average in homeruns.
What the committee did find is that there was a change in the Drag Coefficient when the baseball is in route to the stands. This means that baseballs are interacting differently with the air as they travel to homerun territory. The report states, “Procedures performed experimental tests at Washington State University 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” But how? The committee tested changes in the size, texture, weight, and seam height in the baseballs, but found no correlation with any of a baseball’s physical properties.
Basically, we still don’t know exactly what is causing the surge. We know it’s not the Coefficient of Restitution, or bounciness. We also know that it’s not a collective change in launch angles, causing the balls to travel further. Lastly, we also know that the physical properities of baseballs have remained the same. Rather, it has something to do with how the ball is suddenly more aerodynamic, or the decrease in Drag Coefficient. This could mean that there must be something the committee missed as far as testing methods, or even overlooking another component of the baseball that has been yet thought of being experimented. As of now, the cause is pure speculation. We at least know what it isnt.
Baseballs are still being tested and an interesting hypothesis has now surfaced. What if the core of the ball, or the ‘pill’, is somehow all of the sudden slightly off centered? This causes the ball to spin further into the direction its going, also making it travel further. Rawlings is currently creating baseballs with off centered pills to test this hypothesis.
You can access the Report of the Committee Studying Home Run Rates in Major League Baseball here.