The Significance of Pitching to the Park

This post isn’t about Ervin Santana, who remains a free agent. This post was inspired by fly-ball pitchers, and, interestingly, Santana is no longer one of those, despite his reputation. Definitely, he’s still somewhat homer-prone, but his groundball rates have been creeping up over a few years. He’s pretty neutral, but still, people see him as this fly-ball guy, and so as rumors have flown around, people have questioned the wisdom of certain places being potential destinations. Would you really want a fly-ball guy in, say, Baltimore? Would you really want a fly-ball guy in Toronto? Those are pretty homer-friendly parks. In theory, they’re not suited to Santana’s skillset.

So there’s a question to research: how much does it matter? How much are fly-ball guys hurt by homer-friendly parks? How much do fly-ball guys benefit from non-homer-friendly parks? Beyond the simple park factors, of course. Everybody gives up more homers in more homer-friendly parks, but we know how to adjust for that. What can we say about fly-ball pitchers after that adjustment, for example? Hopefully, you follow. If not, well, I’m still typing. Maybe you’ll start following soon.

Step one of the process: find the pitchers. I isolated all individual pitcher-seasons of at least 100 innings from between 2002-2013. I removed the guys who changed teams somewhere in the middle of the year, leaving me with a still-big sample. I sorted the pitchers by fly-ball rate and for each of them I calculated a z-score. I intended to research fly-ball pitchers and non-fly-ball pitchers. The former were defined as guys with a fly-ball rate at least one standard deviation above the mean. The latter were defined as guys with a fly-ball rate at least one standard deviation below the mean.

Step two of the process: link the pitchers to their home ballparks for each season. Did they pitch half the time in homer-friendly parks? Did they pitch half the time in more pitcher-friendly parks? I was interested in ballpark home-run factors, and we have that information available right here on FanGraphs. I collected all the data for each year between 2002-2013, and I linked each pitcher to the appropriate home park dinger factor. The higher the dinger factor, the greater the rate of dingers.

Step three of the process: more sorting and more averaging. There will be two tables: one for fly-ball pitchers, and one for groundball pitchers. The first has a total sample size numbering 284 pitcher-seasons. The second has a total sample size numbering 242 pitcher-seasons. I decided to split each into three groups, in descending order of ballpark dinger-proneness. This has all been a salad; now it’s time for the meat.

FLY-BALL PITCHERS

Park	ERA	xFIP	FB%	HR/FB	K%	BB%	FB, z	Park, z	RA9/850
HR-friendly	4.48	4.51	45%	11.0%	18%	8%	1.4	1.0	2.2
Neutral	4.24	4.53	45%	9.8%	18%	8%	1.4	-0.3	2.9
Non-HR-friendly	4.16	4.54	45%	9.2%	18%	8%	1.5	-1.0	3.0

All the groups are about equal in quality, with roughly equal strikeout rates, walk rates, and xFIPs. Obviously, the guys in homer-friendly parks have allowed a higher average ERA, and a higher average HR/FB%. But what do the numbers look like after the park adjustments? That’s where the last column comes in, which puts RA9-WAR over 850 plate appearances, or the equivalent of 200 innings. Between the first group and the third group, there’s a difference of about 0.8 wins, or a handful or two of runs. As expected, fly-ball pitchers have been hurt by dinger parks, and they’ve benefited from non-dinger parks. But there’s nothing extreme, here — it’s just a matter of percentages.

How about the other extreme?

GROUNDBALL PITCHERS

Park	ERA	xFIP	FB%	HR/FB	K%	BB%	FB, z	Park, z	RA9/850
HR-friendly	4.07	3.94	26%	11.3%	16%	8%	-1.6	1.1	3.2
Neutral	4.05	3.87	25%	11.9%	16%	7%	-1.7	-0.2	2.7
Non-HR-friendly	3.91	3.91	26%	10.3%	16%	8%	-1.5	-1.1	2.8

Again, pretty similar groups, with similar rates and similar xFIPs. Between the first and third group, there’s a smaller spread in the HR/FB% column, but then there’s something strange going on in the neutral-park group. There’s a suggestion that, when groundball pitchers allow home runs, they’re hit with a little more authority, so the park is a little less of a factor. Look over to the last column. Groundball pitchers have been the most valuable in homer-friendly parks, and the least valuable in more pitcher-friendly parks. That’s what we’d expect, and the difference is also slight. It’s a few runs, per 850 batters faced.

Once again, the conclusion feels obvious. Groundball pitchers are affected less than fly-ball pitchers by ballpark home-run rates. In a homer-friendly park, you want to prioritize finding grounders. In a non-homer-friendly park, fly-ballers can benefit. I could’ve told you this before all the numbers and before all the research. But the bigger point is that nothing should be exaggerated. It’s not whether or not a pitcher is a fit. These things aren’t black and white. It’s not like Baltimore should never acquire a fly-ball pitcher. It’s just that a fly-ball pitcher will have a little less value in a homer-friendly park than he would otherwise. There can be a real difference in value, but it’s seldom enormous.

Let’s take a hypothetical fly-ball pitcher. Over a full season, he allows 300 fly balls (2010 Ervin Santana yielded 292). Split that in half to cover the fly balls he allows at home. So, 150. In a neutral park, maybe 10% of those leave, so, 15. In a more extreme park, maybe 12-13% of those leave, so, 19. That’s a difference of four dingers, or about seven runs or so. Then you apply a park adjustment, because everyone would allow more dingers in the park, and the difference is reduced into a fraction of the whole. It’s easy to say no fly-ball pitcher belongs in a homer-happy park. But, the last five years, Blue Jays pitchers have allowed a dinger at home once per 8.1 fly balls. A’s pitchers have allowed a dinger at home once per 12.5 fly balls. These represent the AL extremes. Most fly balls wouldn’t be homers anywhere. Many homers would be homers everywhere. It’s a fraction of all fly balls that depend on a ballpark, and then after you apply regular park adjustments, it just doesn’t make sense that a guy would thrive in one place, and get annihilated in another. That’s an exaggeration. By far the biggest driver of success is the actual quality of the pitcher himself. Park environment makes a smaller contribution.

Obviously. I’m glad we could do all this to establish what we could’ve and should’ve already known.