Are MLB Baseballs "Juiced?"


The MLB single season home run record has been broken with about two and a half weeks remaining in the season. Rawlings has been the official manufacturer of the baseball since 1977, and MLB was involved in a deal to purchase Rawlings in 2018.

1: With home runs noticeably on the rise around the All-Star break, Rob Manfred stated that MLB did not order or direct a difference in the baseball, but he also noted initial studies have shown there does appear to be less drag.

2: Is the ball juiced?

We’ll use a baseline year of 1977 going forward, and we’ll start by looking at the average number of home runs per team per game, when the average number of home runs per team per game was 0.87. Since then, it has gotten as low as 0.64 in 1981 and as high as 1.26 in 2017 when the previous league-wide home run record was set. The number is at 1.40 this year which puts the league on pace to hit 6,804 home runs.

*Figure 1: MLB Home Runs per Team per Game since 1977. Data from Baseball-reference.com

The totals are up, but is this increase something that could have been predicted? From 2018 to 2019, there was a year over year increase of 0.25 home runs per team per year (22 percent), which is the second largest increase in magnitude (fourth in percent) in this time frame - behind only the 0.29 increase seen going into the baseline year of 1977. The 63% increase from 0.86 in 2014 to 1.40 in 2019 is the largest increase in both magnitude and percent over any six season stretch. The next closest increase in this time span was 51% from 1992 to 1996 (steroids?). Once they reached 1996 levels, home runs held within 10% percent year over year until the dip in 2014, so it makes sense as to why the changes we are seeing today are standing out.

This helps frame the situation, but it doesn’t really say whether the ball is to blame or not. One theory for the increase could relate to players swinging for the fences. Strikeouts have been increasing every year since 2005, and there has not been a steady increase in home runs. More strikeouts also mean fewer balls in play and fewer opportunities for home runs. It’s possible the overall strikeout mentality has increased home runs over time, but it is unlikely to cause this spike in home runs.

Another possible explanation is the focus on hitting analytics and concepts like launch angle and exit velocity in MLB. Baseball Reference has data available since 1988 for a stat that calculates the percentage of fly balls and line drives that were hit in the outfield that ended up as a home run. From 1988 to 2018, the average was 7.7% and the maximum was 9.9% in 2017. The number went down to 9.1% in 2018, and in 2019, 10.9% of airborne balls in the outfield are ending up as home runs. It’s fair to say analytics could have had an impact over the course of a few years. I just don’t see how the league as a whole would have set the home run record, gotten worse, and then gotten better on execution and analytics alone.

The commissioner said the ball seems to have less drag this year, and I would support that theory or the theory in general that the ball is juiced. Many variables could impact the home run totals year over year, and assuming the ball is the same next year, there is no telling if the home run total will go up or down, but it will be a topic of conversation.

1. https://www.wsj.com/articles/newell-brands-to-sell-rawlings-brands-for-395-million-1528203488

2. https://www.espn.com/mlb/story/_/id/27155532/manfred-mlb-alter-baseball-more-hrs


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