Friday, April 30, 2021
Introducing Statcast Park Factors
There’s lots in there, so let me pick out a few things. At Great American Ballpark, 2019-2021 there were 375 HR hit. In Reds games away from GABP, there were 293 HR hit. That’s a nominal factor of 375/293 = 1.28 times, or 128 in the index=100 parlance. Now, we apply additional adjustments for the Reds batters and pitchers. While we did limit the look at Reds games at GABP and away from GABP, you can still get disproportionate usage of players. Votto may play all the time at home and away, but Luis Castillo may not. In addition, even if Votto plays all the time home/away, he may not face the same distribution of LHP/RHP. And naturally, we’d base it on a per plate appearance basis. Once we account for all that, the three-year rolling average for GABP HR is 133.
And it’s not just HR. Want to know the toughest place to strikeout? That’s Coors and Kauffman. High elevation parks will do that for you. Want to know the three year rolling park factors for Fenway for all the metrics going back to 2001? That’s there too.
We also show the impact of parks on HR-type of distances. We looked at all batted balls hit at 24 to 32 degrees, launched at 90+ mph. We then standardized them to 28 degrees, 100mph, at 74 degrees F, 500 feet of elevation. We can therefore account for a naive effect of temperature and elevation on each park. In addition, dome/roof parks have a bit better carry, so we adjust for that too. Everything else that is unaccounted for lands in a “environment” bucket, which could be the effect of wind (think Wrigley) or the effect of humidity at that park (over and above temperature and elevation) or simply Random Variation (especially if you are going to look at 2021 with so few games played).
We don’t include any kind of reversion to the mean, or ballast, which you should if you want to create “true” park factors. That said, we highly recommend just using the three-year park factors, as that would essentially act as a ballast. That that said, the data is all there, so the researcher can create their own version for their own needs.
And if you want to learn even more, here's a terrific piece from Mike.
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