MLB Regression Report: Identifying the 'dead ballparks'

By Adam Burke  (VSiN.com) 

May 25, 2022 08:48 PM
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The start of every baseball season presents challenges because of all the roster turnover and the adjustments that players make, but what really increases the degree of difficulty with MLB is that the playing object is fundamentally different year in and year out.

The big change this season was that Major League Baseball installed humidors for the baseballs in all 30 parks. What started with Coors Field and then expanded to Chase Field went up to five parks, then 10 and now all 30. John Shea of the San Francisco Chronicle wrote in his May 15 article that “the humidor is designed to store 200 dozen balls for at least 14 days at 70 degrees Fahrenheit and 57% relative humidity averaged over a 24-hour period. The exception is the Coors Field humidor, set at 65% humidity.” 

Let’s start with the fundamental flaw of this idea from MLB. While the humidor standardizes humidity for the storing of the balls, it does not account for the differences in climate and environment around the United States. The humidity and atmospheric conditions in Atlanta are much different than Boston, which are different from the conditions in Seattle, San Francisco, Kansas City, Tampa, etc. 

We are about six weeks into the MLB season and temperatures are warming up across the country, but we’ve seen offensive numbers in cold-weather cities dramatically affected by the new baseballs and the humidor. The thought from a lot of people that are more in tune with the science than I am is that offense should pick up as it gets warmer and more humid across the country. Baseballs generally travel better in the summer months, and the effects of the humidor should be lessened. That is not a guarantee, but we have seen the league-wide HR/FB% go up from 10% in April to 11.2% in May, so that may be an indication of more power. 

Statcast data from BaseballSavant.com provides a lot of outstanding insight into what is happening on a pitcher and team level. In this week’s Regression Report, rather than look at teams and individual pitchers, I thought it would be fun to look at ballparks. 

Across the league, the difference between actual stats and expected stats is down. Statcast uses historical data on exit velocity, launch angle, batted-ball type and other factors to determine the expected batting average and slugging percentage of a batted ball. This season is an outlier with the humidor and a “dead ball,” but the data (through Sunday’s games) is quite significant. 

Batting averages 

Actual BA: .236

Expected BA (xBA): .254

Difference: -.018 

Slugging percentages

Actual SLG: .380

Expected SLG (xSLG): .437

Difference: -.057

To give you an idea of how big of a difference this season is, here are the BA-xBA and SLG-xSLG numbers for the other Statcast-era seasons dating to 2015:

2015: .009 / .015

2016: .007 / .012

2017: .006 / .012

2018: .006 / .010

2019: .005 / .011

2020: .000 / .002

2021: .001 / .003

2022: -.018 / -.057

This is the first season in the Statcast era in which the actual BA and SLG are lower than the xBA and xSLG. Also, as you can see, this year’s discrepancies are also the largest of the data set by a big margin. With five previous seasons' worth of data and expectations, you can see that in 2020 and 2021, Statcast data was extremely accurate, but 2022 has been the outlier of all outliers. 

Speaking of outliers, some parks have been bigger culprits than others. There are only four ballparks in which the BA-xBA is on the positive side and those are in Cincinnati, Denver, San Francisco and Los Angeles (Dodgers). The only park on the positive side in SLG-xSLG is in Cincinnati. Not surprisingly, Coors Field has the smallest discrepancy on the negative side at -.016.

My focus in this week’s Regression Report is to look at “barrels.” A barreled ball has an xBA of at least .500, an xSLG of at least 1.500 and is hit at least 95 mph with an optimal launch angle range based on the exit velocity. Basically, think doubles, triples, home runs and deep fly balls. Most barrels end up with those outcomes, and that type of contact is the most hurtful for pitchers. This season, even with offense depressed around the league, a barreled ball has still yielded a batting average of .690 and a slugging percentage of 2.252.

Here’s the problem — this season’s barreled balls have an xBA of .801 and an xSLG of 2.770. If you want to know why runs and offense are down, this is a big reason.

Certain ballparks are larger culprits in this equation and you’ll notice a pattern with those are on the list:

Highest Difference in BA-xBA on Barrels

Comerica Park (DET) -.265

Progressive Field (CLE) -.223

Oriole Park at Camden Yards (BAL) -.198

PNC Park (PIT) -.188

Minute Maid Park (HOU) -.185

Highest Difference in SLG-xSLG on Barrels

Comerica Park: -1.123

Progressive Field: -.906

Oriole Park: -.903

Yankee Stadium -.797

PNC Park -.778

The first thought is that a lot of those offenses are pretty bad, right? The Tigers and Pirates are awful, the Orioles aren’t very good and the Guardians don’t make a lot of quality contact despite some of their early-season offensive explosions. The Astros and Yankees are big outliers on this list given their contact quality and talent.

Remember, though, that this is by venue, which means we’re also looking at the visiting teams, too.

Detroit, Cleveland, Baltimore, Pittsburgh and New York are all cold-weather locales early in the season. Fenway Park was pretty high on this list until the Red Sox had some offensive breakouts. Not all cold-weather cities have been affected the same. For example, Target Field in Minneapolis has the 10th-lowest gap. Wrigley Field is in the top five, but the wind plays a huge role there.

But my read on this situation is that we have some teams perceived to be bad offensively that should see an uptick in offensive production as the weather warms up. Similarly, some teams perceived to be good, like the Astros and Yankees, could also see gains. The humidor has affected offense as a whole but has done so disproportionately to this point in the season.

Sportsbooks have adjusted their totals downward to account for the new environment but may not be as quick to adjust with some teams and some ballparks as the weather warms up, so keep that in mind.

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