Park-Adjusted Pitcher Strengths of Schedule

In my previous article, I created an approach to examine pitcher strengths of schedule by aggregating the hit frequency projections of the hitters they faced. So, for example, Dee Gordon was projected to hit 0.229 singles, 0.032 doubles, 0.015 triples, etc. against right-handed pitchers when he faced Stephen Strasburg in the first plate appearance of the season. By adding together all of those fractional singles, doubles, and other possible results, I was able to calculate an expected wOBA for pitchers based on the quality of the batters they faced.

If you think of the differences in expected wOBA as schedule luck, then that initial research suggested that the difference between the luckiest and unluckiest pitcher so far in 2017 was pretty small. The former was Patrick Corbin, whose batters faced combined for a .324 projected wOBA against left-handed pitchers. The latter was Ricky Nolasco, whose batters faced combined for a .337 projected wOBA against right-handed pitchers. That difference of 13 points of wOBA is the same as the difference between Kyle Seager and James Loney. It’s something, but it isn’t huge.

But several commenters correctly pointed out that labeling those expected wOBA differences as pitcher luck overlooked some critical variables that influence a pitcher’s success, the most prominent of which is park factors. A Rockies starter could face a lineup full of James Loneys every day in Coors Field, and Loney’s moderate power would undoubtedly turn into some real extra-base damage in a park that is conducive to that. For this article, I aimed to capture those park differences.

There are actually two places in my approach that call for a park adjustment. The first is in the projection of hitter result frequencies. By virtue of hitting so often in Coors Field, Rockies hitters were seeing an overestimation of their chances for extra-base hits, and so I adjusted the three-year window of actual results hitters had that I used to project their result frequencies to be park-neutral. Then, for the 2017 plate appearances I was running for the strength-of-schedule model, I park-adjusted the park-neutral projected result frequencies for the park that game took place in. For a game in Coors Field, that would increase extra-base hits. For Gordon in the season opener in Miami, it would reduce his already meager home run total.

About two-thirds of the way through 2017, those park differences proved to be more extreme than the biggest differences in the quality differences of batters faced.

Man, being a Coors starter is brutal. I limited these tables to qualified starters, and the Rockies have three: Antonio Senzatela, Kyle Freeland, and Tyler Chatwood. All three have suffered the most from the parks they’ve pitched in, with Senzatela seeing a nightmarish 21-point increase in the projected wOBA of his batters faced because of the parks he’s pitched in. Senzatela has allowed an actual wOBA of .333 to the batters he’s faced, which is 18 points better than his park-adjusted expectations. That’s hardly in the Chris Sale (96 points) and Max Scherzer (84 points) territory, but it is the same difference as Jake Arrieta, Mike Leake, and Drew Pomeranz and better than pitchers including Jose Quintana (15 points), Jon Lester (14 points), and Justin Verlander (5 points) who all have had easier parks to deal with.

None of the pitchers helped by their parks has seen a correspondingly big benefit to what the Coors starters have seen in disadvantage. However, this perspective should hopefully easy Nolasco’s concerns. He’s offset much of the disadvantage he’s faced in strong opposing hitters by facing them in pitcher-friendly parks.

Combining the effect of the parks they’ve pitched in with the quality of the batters they’ve faced, pitchers at the extremes have seen significant differences in their schedule fortune so far in 2017.

The spread from luckiest to unluckiest is 30 points of expected wOBA, but even if you throw out the Rockies starters that you would likely never consider in a Coors start in fantasy, there are several important fantasy starters who have seen a difference in schedule luck of around 15 points of wOBA so far this season. The most notable fortunate starter is probably Jason Vargas, the unexpected All-Star for the Royals. Even following some poor July outings, Vargas is still sitting on a 3.00 ERA for the season, and his .283 seasonal BABIP is just one point off of his career mark. This schedule analysis is providing an explanation of some of the difference between Vargas’ ERA and his FIP and xFIP, which are both north of 4.00.

On the other side of things, I should probably note that the park-adjustments I made are regressed, but even still, Atlanta’s new SunTrust Park looks like a hitter’s haven. Meanwhile, Luis Severino and Zack Greinke have been succeeding despite their circumstances. It’s not fair to expect their luck to completely turn around the rest of the way—after all, they won’t be changing home parks or divisions. By this should at least provide an interesting perspective for pitchers who change teams in the offseason.