Minute Maid Park a surprising haven for pitchers

Houston's Minute Maid Park has a reputation as an extreme hitters' park, for easily understandable reasons: The famous "Crawford Boxes" in left field are a mere 315 feet away down the line, making it an enticing target for right-handed hitters. The softest-hit homer of 2018 so far was hit in Houston. The softest-hit homer of '17 was hit there, too. (As were three of the top five, and five of the top 10.) You remember Game 5 of the World Series, right? You don't have to go deep to go deep here.
With that as a backdrop, allow us to make a case similar to the one we made last offseeason when we explained why Detroit's massive Comerica Park is actually more favorable to hitters, not pitchers: Minute Maid Park isn't a hitters' park at all. It's a pitchers' park, or at least it plays like one. 
If that sounds crazy, we understand. It sounded crazy to us, too. But after digging into the numbers, it's difficult to overlook what's actually happened in Houston.
Before we dig into the complicated stuff, let's start with the simple stuff. Let's just look at a traditional stat -- runs scored. Since the start of 2017, the Astros have scored 538 runs at home, the 15th-highest home total in the game. In that same time frame, they've scored 747 runs on the road, which isn't just first, it's first by a lot. That's a whopping 170 more road runs scored than the second-place Braves. 
That means that the Road Astros have outscored the Home Astros by 209 runs, which is a massive difference. Nineteen of baseball's 30 teams have scored more runs at home, with the overall average being a plus-16 runs scored advantage at home, owing to baseball's built-in home-field advantage. Not the Astros, however. This is already not how you'd expect a team that calls a supposed "hitters' park" home to behave.

It's not quite as stark from the pitching point of view, but it's a similar effect. Houston pitchers have allowed 441 runs at home, the third fewest, while giving up 491 on the road, the ninth fewest. Only six teams have a larger gap between home and road, on the pitching side.
In fact, this trend holds steady across a variety of stats. Since the start of 2017, Astros batters have performed worse at home to the tune of …
-.017 of batting average (.268 home, .285 road)
-.022 of batting average on balls in play (.298 home, .320 road)
-.019 of on-base percentage (.333 home, .352 road)
-.034 of slugging percentage (.447 home, .481 road)
All four gaps are the second largest in baseball, second only to the Mets.
That's what it looks like from a team perspective. But what about from a player perspective? Whenever it's suggested that Houston may play in a pitchers' park, the natural reaction is to say "well, of course it's hard to score runs there, the Astros have Justin Verlander, Gerrit Cole, Charlie Morton and a potentially historic rotation." If we just compare the home and road performance of players to themselves, then we can do a little to get past the issue of whether it's just about talent.
The way we'll do that is to look at all Houston batters who received at least 200 plate appearances both at home and away since the start of 2017, which gives us 10 players, and all Astros pitchers who faced at least 130 hitters both home and away which gives us 10 more. (For Verlander and Cole, we looked only at time with Houston, and we excluded the since-traded Joe Musgrove and Mike Fiers.) We'll judge them based on wOBA, which is just like OBP, except that it gives more credit for extra-base hits.
Of the 10 Astros hitters, seven have performed better on the road.

Most notably on that list is Jose Altuve, who has hit well at home since the start of 2017 (a line of .300/.357/.428, giving him a .340 wOBA that is the same as César Hernández or Mike Moustakas), but has hit a monstrous .386/.450/.608 line on the road. The resulting .446 wOBA from that is basically Mike Trout, who has a .451 mark. That's how good Altuve has been away from Houston.
In fact, the 106-point gap between home and road for Altuve since the start of last year is the largest of any player in baseball, at least among the 276 players with 200 plate appearances both at home and on the road. Evan Gattis, who has been below average at home and a star on the road, is 10th on that list. Brian McCann is 18th and Alex Bregman makes the top 50, too.
How about the pitchers? Eight of the 10 Houston arms we've looked at have been better at home.

For Verlander -- again looking only at his time since being traded -- the difference is huge. On the road, he's been very good, allowing a .176/.233/.304 line and a 1.34 ERA, and his .236 wOBA would by itself make him the equivalent of Jacob deGrom.
But Verlander, at home? We don't really have the words for this. He's got a .142/.187/.264 line against, and a miniscule .198 wOBA. To put that into context, only a dozen pitchers in the past decade has had a season of at least 50 innings and a wOBA lower than that, and they were all one-inning relievers like Craig Kimbrel and Mariano Rivera.
So now that we've shown that it might actually be more difficult for hitters to produce in Houston, the inevitable question is: Why? How in the world is a park with that short porch hurting an offense this much?
Maybe it's the approach -- that the short porch is a little too enticing.
"Altuve was telling me that when he goes home he tries to go deep, and when he goes on the road, he hits .400," Colorado outfielder Carlos Gonzálezsaid last year to MLB.com.
"I don't know if it's subconsciously we see the [short left-field] porch, the Crawford Boxes [at Minute Maid Park] and try to hit the ball out of the ballpark," said manager AJ Hinch last month. "It's weird, it's very unusual."
But the numbers don't really back that up. Altuve has pulled 36 percent of his batted balls at home in 2017-18, which is less than his 42 percent on the road. As a team, Houston hitters have pulled 41 percent of balls home and away. There's not a meaningful difference in strikeouts or walks, either.
Whatever it is that's happening in Minute Maid, it appears to be something of a recent thing, because for years, there wasn't a real split in home vs. road performance, at least for the Astros' offense -- contrary to the park's reputation.
(This was known if you were looking in the right place. Here's the Houston Chronicle in 2011, with the headline "Hitters' haven or pitchers' park? Numbers show Minute Maid fair to both." Here's The New York Times way back in 2005, pointing out that "Minute Maid is an almost perfectly neutral park for run scoring.")
For years, that was true, almost precisely so. From 2005-14, the Astros scored 4.1 runs per game at home, and they scored 4.0 runs per game on the road. In '15, as the new young core with players like Carlos Correa and George Springer arrived, their production shot up evenly, scoring 4.5 runs per game both at home and on the road.
In 2016, that very much stopped being true. Over the past three years, Astros bats have scored 4.4 runs per game at home and 5.7 per game away from Houston.
 
This is where it gets unsatisfying, because we're left with only suggestions. There were theories about the impact of the new lights installed prior to 2016, and of course the removal of "Tal's Hill" in center field after '16 meaningfully changed the dimensions in that part of the park, though that doesn't explain what happened during '16 itself. The roof being open or not can have an impact, though at 13 times open last year and 11 so far this year, they're not doing it more or less than they have been over the years.
We even looked into the fact that the short porch may simply limit the amount of space available for balls to fall in. That much is true; the average Houston left fielder is only 131 feet from the center fielder, well below the average of 143 feet and far below the Major League high of 154 feet at Kansas City's Kauffman Stadium. The large 2017-18 gap between the Astros' .320 road BABIP and .298 BABIP may have something to do with that, but again, that's not new.
If there is something we can see in the 2017-18 numbers, at least for Houston's lineup, it's that at home, it does worse at the two things most likely to generate success: hitting the ball hard and in the air.
At home, the Astros hit the ball on the ground 44.5 percent of the time. That's nearly three points higher than they do on the road, which is the largest gap in baseball. At home, they have a hard-hit ball (those with 95 mph of exit velocity or more) on 33.9 percent of their batted balls, which is nearly three points lower than they do on the road. That's also the largest gap in baseball. 
We know something's changed, but it's not clear what. Maybe it's the batter's eye, which has been adjusted at least once since it was installed for 2017. Maybe it's the lights, or the psychology of the short porch looking so close, or something we can't guess at all. Either way, the park that allows baseball's easiest homers doesn't play like you think it does. It doesn't boost offense, aside from a few cheap dingers. It might be just the opposite.