Yankee Stadium is a hitter’s park. A bandbox. A little league field. A place where the fences are so short that even I, who can remember each extra-base hit from my youth and high school baseball career after the age of 13, could perhaps slip one over the fence. (Still was all-conference as a pitcher, haters.)
This is not what the numbers say.
Park factors have been around a long time, doing their darnedest to help the baseball industry quantify how much extra money Rockies pitchers should get during arbitration and what exactly happens when you plant a 37-foot wall in the middle of left field because it’s 1934 and your ballpark has run into the street. The concept behind them is pretty simple—compare what happens at a given park to what happens at all the other parks, adjusting for the teams who’ve played in each, if not the specific hitters or pitchers, if not the specific exit velocities and spin rates and other physics-al data from the flight of the baseballs themselves.
It’s this range of “adjusting” that I’d guess gives various sources of Park Factors their discrepancy. ESPN’s Park Factors page, a seemingly unmaintained relic from a bygone era of digital sports media which nonetheless updates with fresh statistics every day, rates T-Mobile Park in Seattle near the league median so far this season in terms of friendliness to hitters/pitchers. Statcast, meanwhile, rates it as the third-friendliest in baseball. Is this a sample-size thing, the effect of looking at hardly half a season of data? Probably, at least in part. But that’s a fairly wide gulf to indiscriminately chalk up to sample size. A more plausible explanation is that there’s at least some sort of fundamental difference in the formulas, though I believe even Statcast’s isn’t entirely based on contact data.
The genesis of this post comes from Giancarlo Stanton. If you pull the data for MLB’s 152 qualified hitters from FanGraphs and compare wOBA (a comprehensive offensive metric which does not account for park factors) to xwOBA (a comprehensive offensive metric designed to say how good a hitter would be if their contact always yielded the average result, given its exit velocity and launch angle), Stanton comes out as the second-unluckiest hitter in baseball. At first, I thought this was a Stanton thing. Metrics often have a difficult time adequately measuring outliers, and Stanton, who routinely finishes in the top six in the sport in average exit velocity, is definitionally an outlier. He hits the ball harder than just about anyone. He does it year after year. “Average” results for balls hit 115 miles per hour are hard to come by.
It’s possible this is part of what’s happening, and there’s certainly something going on with Stanton’s xwOBA, given he outpaces all of his teammates in “bad luck,” measured this way. Maybe it’s the outlier thing. Maybe it’s the shift. Still, it’s weird to see a home run hitter who plays half his games at Yankee Stadium rated as the second-unluckiest man on the face of the baseball-playing earth. And I don’t know if this makes it weirder or less weird, but just as there’s certainly something going on with Stanton, something sure seems to be going on with Yankee Stadium as well.
I went back to FanGraphs and pulled every hitter’s wOBA and xwOBA for the season so far, alongside their quantity of plate appearances. Then, as best I could, I converted these to team numbers. What does this mean? I estimated each team’s combined wOBA and xwOBA based on the sum of their parts—weighting by plate appearances, I averaged players’ data over the season to date. Naturally, there were flaws: In addition to this being a bit of a crude estimate mechanism, it excluded the 22 players with plate appearances with multiple teams this season (593 players have registered at least one plate appearance), Carlos Santana most notable among them, as partial-season xwOBA is not, to me, available. This wiped out 1.8% of plate appearances in the sample, a non-trivial amount. I also couldn’t include players with no xwOBA, a constraint which only resulted in the removal of Brent Rooker, who went 0 for 3 on Saturday for the Padres in his season debut. All these caveats included, the Yankees came out as the third-unluckiest team so far this year offensively. Which—alongside the fact all ten of the ten unluckiest teams were in the American League, and alongside the fact that every single team came out as “unlucky” to at least a tiny extent (I think this has to do with how FanGraphs scales xwOBA, but I haven’t found a recent explainer from them, so that impression may come from a flawed memory or could simply be outdated)—made me think I’d messed up. Which is how I ended up comparing Statcast’s Park Factors with whatever the formula is over at ESPN. Both of which have Yankee Stadium as the park second-most favorable to pitchers this year. Not hitters. Pitchers. What in the holy hell?
Looking back over the last few years, this isn’t anomalous. By ESPN’s count, Yankee Stadium’s been a pitcher’s park in three of the last four seasons, with the lone exception coming from the wacky 2020 campaign. (You want to talk about a small sample…) Statcast yields the same result. In some years, home runs have been up but the overall park factor has remained down, but in others, including both this year and 2019, eliminating the possibility this is driven by baseball’s pivot to humidors at all parks, home runs have actually come out as less likely to happen at Yankee Stadium than elsewhere. This is easy to gut-check, which leads one to the surprising finding, when one looks at splits, that the Yankees themselves have hit only four more home runs at Yankee Stadium than they’ve hit on the road so far this year despite playing the same number of games at home and away.
It’s fair to remain skeptical of the claim that Yankee Stadium is “a pitcher’s park.” With the exception of Tropicana Field, the various recent homes of AL East teams (Dunedin, Buffalo, Toronto, Baltimore, Boston) have been kind to hitters, which could shape some of these comparisons, and the sample size question is legitimate: It’s possible we should be using longer averages than the three-year mark to which Statcast defaults, at least in situations where it’s possible. It could be that this has something to do with weather—perhaps 2019 was an unusually cold year in New York, and as this summer goes on, perhaps Yankee Stadium will climb the 2022 rankings. It could be that park factors aren’t deserving of much confidence overall right now, given the inconsistency of the baseball, the inconsistency of the season’s calendar, the inconsistency of crowds, etc. during recent years. It’s possible Yankee Stadium’s pitcher-friendly score says more about those various inconsistencies than about Yankee Stadium.
Still, it’s one thing to say, “Giancarlo Stanton probably hasn’t been that unlucky,” and it’s another to say, “Giancarlo Stanton’s actually been lucky.” I don’t think you can say Yankee Stadium’s a hitter’s park. Not without some better data to back that up.
