What Happens When You Pitch In Front of the Monster

Lately, Tony has written some pieces touching on the Fenway park factors. Though he’s provided detail, you already had some understanding of how the park plays. The Green Monster is unlike pretty much anything else in the game today, and it changes what happens to balls in play. To right field, and to center field, Fenway is more or less fair, if not a wee bit pitcher-friendly in places. To left field, though, and especially to left-center, balls that would be outs elsewhere clang off the Monster for singles or doubles. Every so often, the Monster will claim a would-be dinger, but that’s little consolation to pitchers; if they give up a ball headed to left, it’s probably putting a guy on base, and maybe in scoring position.

There’s nothing subtle about the Green Monster. You can’t miss it. It’s right there, casting a shadow over everything, and what it does makes absolute sense. Of course it leads to more singles. Of course it leads to more doubles. Of course it makes that part of Fenway hitter-friendly. Pitchers know all about it when they go to work, so I got to wondering, does that in any way change the way the pitchers pitch? I’m going to go ahead and spoil the rest of this article: yes. You already know how. The remainder is just going to confirm your suspicions.

As is frequently the case, this research borrows heavily from Baseball Savant. I decided to examine the window between 2012 – 2014. It’s a big enough sample to diminish most of the noise, and it’s a small enough sample to allow Baseball Savant to still function. So, let’s just imagine. If you were a pitcher, how might you imagine pitching differently if you had the Green Monster in the outfield? Odds are, you’d try to keep the ball away more often against righties. Odds are, you’d try to keep the ball in more often against lefties. You don’t want righties to be able to pull the ball; you don’t want lefties to be able to serve the ball over to left or left-center.

So I created a box. I decided to look for pitches over the outer third or beyond against righties, and pitches over the inner third and beyond against lefties. It’s the same box. Overall, in Red Sox home games, 41% of pitches were thrown somewhere within that box. Overall, in Red Sox road games, 37% of pitches were thrown somewhere within that box. That might strike you as a small difference, but it’s a difference of four percentage points, which is the greatest positive difference in baseball. In second place, we find a Dodger Stadium effect, at three percentage points. Only one other ballpark is north of two percentage points. It’s not surprising to find this, but it’s nice to know for sure.

Now we can break it down by handedness. Let’s consider right-handed batters, only. The relevant data, in easily consumable form:

• Red Sox home games: 51.4% pitches over outer third or beyond
• Red Sox road games: 47.6%
• Difference: +3.9%
• MLB rank: 1st

Clearly, pitchers have stayed away from righties to a certain extent. Possibly of some interest: against Red Sox hitters, the difference is +3.2%. With Red Sox pitchers, the difference is +4.4%. It might be nothing, or it might be the slightest little hint of the Red Sox having a better understanding of how to pitch in their own ballpark.

Now, let’s consider left-handed batters, only, and go through the same stuff.

• Red Sox home games: 29.1% pitches over inner third or beyond
• Red Sox road games: 25.0%
• Difference: +4.1%
• MLB rank: 1st

And, again, as expected, pitchers have stayed in more often against lefties to a certain extent. Once more, we see a bigger difference for Red Sox pitchers than for Red Sox hitters, although the gap is smaller than earlier. Maybe a hint of something; maybe a misleading hint of nothing.

Let’s go back to righties real quick. Not surprisingly, the difference away is mirrored by the difference in. In Red Sox home games, righties have seen 28% of pitches over the inner third or beyond. On the road, that rate goes up to 32%. So nothing really changes in the middle of the plate. There are more targets away, instead of in. It’s not an effect you observe on every single pitch, but remember that pitchers need to be able to remain unpredictable. Batters will pick up on significant shifts. Adjustments for environment need to be subtle.

In Fenway and elsewhere, righties in Red Sox games have seen identical fastball rates. However, of those fastballs, this difference can be observed:

• Red Sox home games: 50% fastballs to righties over outer third or beyond
• Red Sox road games: 46%

And in Fenway and elsewhere, lefties in Red Sox games have seen a slight bump in fastball rate without the Green Monster being in play. And, out of those fastballs, this difference can be observed:

• Red Sox home games: 49% fastballs to lefties over outer third or beyond
• Red Sox road games: 54%

Against a left-handed batter, a fastball away is more likely to be hit to the opposite field. In Fenway, that leads to the Monster. Against a right-handed batter, a fastball away is more likely to be hit to the opposite field. In Fenway, that leads away from the Monster. So these are more perfectly intuitive splits. Pitchers and catchers know what’s out there, so they want to do what they can to stay away from it without overhauling everything.

Feel like getting individual? Here’s how David Ortiz was pitched in this past season, split at home and on the road:

Dustin Pedroia also makes for an interesting example. Some data:

Season	Home, Away%	Road, Away%	Difference
2008	50.0%	43.8%	6.2%
2009	50.1%	42.9%	7.2%
2010	47.7%	44.3%	3.4%
2011	51.7%	44.1%	7.6%
2012	54.4%	45.4%	9.0%
2013	49.0%	45.1%	3.9%
2014	41.5%	43.6%	-2.1%

Used to be, pitchers stayed away more often against Pedroia in Boston. As recently as 2012, he saw 54% pitches away at home, and 45% pitches away on the road. But this past season, the split eroded, and pitchers actually attacked Pedroia in more often at home. Pedroia, of course, was hurt, and he wasn’t much of a power threat. Perhaps the perception was that he was trying too hard to knock balls off the Monster. Anyhow, here’s a .gif of what Pedroia’s 2012 split looked like:

There’s nothing in here you couldn’t have guessed, probably, but it’s interesting to me to see confirmation. There are park effects, and, sometimes, there are responses to park effects, and this is the latter — this is pitchers behaving differently specifically because of a unique pitching environment. The differences aren’t enormous, but they can’t be, because pitchers can’t have batters knowing what they’re likely to get, and where they’re likely to get it. If you figure that people pitch mostly optimally, then it follows that pitches ought to have almost equivalent run values. In order to achieve an equilibrium in Fenway Park, you have to pitch away from the Monster a little more often, because balls in play toward the Monster have a run value that’s through the roof. So pitchers need to protect against that while also staying largely unpredictable, the result being a small shift in tendencies.

Righties, for example, probably know they’re more likely to be pitched away in Boston, but they’re pitched in often enough to keep them honest. So everything becomes equivalent again, and the pitches in are a tiny bit more effective because the righties have a tiny bit higher expectation of a pitch somewhere else. What we’re seeing is a somewhat small effect, and also the biggest such effect in baseball. So relatively speaking, the effect is huge.

I’ll throw this out there here at the end: we see an almost perfectly opposite effect in Rangers games, whether they’re home or away. Pitchers try to pitch away from the gusts that sometimes blow out to right field. That’s a post for another day. For this day, pitchers are observed to pitch with a certain awareness of the Green Monster. Pitchers don’t like the Green Monster, and pitchers pitch like it.