Astros Home Field (Dis)Advantage

“It is a riddle wrapped in a mystery inside an enigma...” —Winston Churchill

Sure, he wasn’t talking about baseball or the Astros. But when I think about the Astros strange Home / Road record, that quote came to mind. So, let’s talk about reasons for the Astros home / road differential. It’s a reverse split, since professional sports teams are expected to have a home field advantage. Some commenters at TCB have suggested that the Astros would be better off with a Wild Card spot rather than Division Championship because they have a home field disadvantage.

Before we make assumptions about the merits of possible playoff seedings, perhaps we need to understand whether a reason exists for the home/road split Currently the Astros have the third best Road Record (behind the Braves and Dodgers), but only the 20th ranked Home Record (close to .500 record). The Astros have a negative run differential at home. If the Astros played as well at home as on the road, the team would be coasting to another AL West Division championship.

I calculated a Home and Road pythagorean record below.

[ In the table above, the negative sign was omitted from the Road Above Pythag Cell.] The Astros should have a worse record at home, compared to actual, based on runs scored and runs allowed. The Astros are playing worse at home than on the road, yet the team has over performed its Pythag at home. The Astros’ record on the road is very good, but the team has actually under performed by almost 3 wins, based on runs cored and allowed. Research has shown that home field advantage in baseball is approximately 54%, a winning probability that has remained stable over decades. Yet the Astros Pythag win record in home games is 49%.

The difference in the winning percent at home and on the road based on Pythag is 0.149, which is pretty incredible. That would be larger than typical home/road win percent differentials, but also even more anomalous because it’s the home percent which is lower. Based on an analysis of team records at neutral sites, a Baseball Prospectus article concluded that no team (other than the Rockies) can support a home field advantage greater than 8% more wins. Yet the Pythag H/R win difference for the Astros is 33%, and it favors the road.

The H/R winning percents for previous Astros seasons (excluding the shortened 2020 season) is shown below.

(Home Win% / Road Win% / Home% Minus Road%)

2022 .679 / .630 / .047

2021 .640 / .553 / .087

2019 .741 / .580 / .161

2018 .569 / .708 / -.14

20l7 .593 / .644 / -.06

In the three recent years, the Astros held a home field advantage, as indicated by a higher win percent at home than on the road. The Astros had a reverse H/R split in 2017 and 2018, with a lower win percent at home. However, in those two years, the home “disadvantage” was not as pronounced as 2023, because the home record continued to be quite successful (well above .500). And it’s fair to say that the Astros are “road warriors” based on those five years and 2023—because they always seem to win at a high rate on the road.

Is the Pitching or Hitting Responsible for Reverse Split?

The answer to this question in brief is “for the Astros, both the hitting and pitching are worse at home than on the road.”

The Astros have the second best offense on the road (114 wRC+) and hit the second most home runs (107) on the road. At home, the Astros have the 15th best offense (104 wRC+) and the 17th most home runs (78). The fact that the Astros hit 29 more home runs on the road than at home (in the same number of games) is particularly notable. The Astros also have the 25th worst BABIP at home (.289), compared to a .300 BABIP on the road (10th). The home run differential also raises the question as to whether the Astros’ team, as constructed, is well suited for the ballpark dimensions at MMP.

On the pitching side, the Astros have the second best ERA (3.66) on the road, but only the 16th best ERA (4.09) at home. The strike out and walk rates are very similar at home and on the road. The team’s FIP is higher than the ERA both on the road and at home. But the gap between ERA and FIP is the highest of any team on the road (-0.65), compared to a 13th ranked E-F (-.08) at home. The Astros’ pitching allows more HRs on the road (91) than at home (83). But the Astros’ pitching on the road allows the lowest BABIP (.279) in the majors. At home the Astros’ pitching allows the 6th highest BABIP (.311).

The telling comparison is HRs hit compared to HR allowed. On the road, the team is +16 HRs, at home the team is -5 HRs Again, it appears that opposing teams are more adept at handling MMP dimensions than the Astros.

The fact that BABIP plays a role, both for pitching and hitting, on the H/R win splits would also support the notion that randomness is involved in the result.

Other Causes?

The factors causing home field advantage have been studied, but the results are somewhere between suggestive and speculative. Here are some of my conclusions/thoughts:

• One of the leading theories of home field advantage is that the officiating is more favorable to the home team. Depending on the sport, there is some support for this theory. Why would the officials show favoritism to the home team? The hypothesis is that referees subconsciously attempt to please the home crowd. So, do the Astros not receive this advantage at home? My answer is “no.” According to Umpire Scorecard, the Astros receive relatively unfavorable balls/strike calls both at home and on the road. However, the favorable calls are worse on the road (36%) than at home (42%).
• I’m not aware of many articles about home field disadvantage, because it is so uncommon. But Freakonomics mentions an academic article suggesting that in some circumstances home field will create a disadvantage, because the home team feels the pressure of supporters. The pyschology professor notes that, given recent research on self-presentation and self-attention, “a supportive audience might engender a state of self-attention that could interfere with the execution of skillful responses.” I don’t know of any way to confirm such an impact on the Astros at home, but maybe we shouldn’t rule it out.
• I also wonder if the home field disadvantage has something to do with weaker performance in the 1st inning or early innings. Unfortunately, I do not have immediate access to scoring data by inning split into home and away. However, my subjective impression is that the Astros may perform more poorly in the 1st inning at home than expected. This could “eliminate” the expected home field advantage. Historically, the first inning and to a lesser extent other early innings, comprise most of the home field advantage. Two Fangraphs articles discuss possible reasons for the first inning impact on home field. Factors related to warming up pitchers are frequently mentioned as a possibility. In a recent broadcast, Astros analyst Steve Sparks suggested that the timing of batting practice on the road vs at home could be a factor affecting home field record.

Are the Astros better off with a wild card due to home field disadvantage?

No, of course not. First, it’s doubtful that any home field disadvantage has a greater impact than the reduction in championship probability associated with playing an extra round of games.

Second, the cause of the home field disadvantage is unknown. The default conclusion is that the inverse H/R split is due to random chance. Given enough opportunities, random chance will result in unlikely results sometimes.

Third, the research indicates that home field advantage is much weaker, or even non-existent, in the playoffs. It’s not uncommon for road teams to win more playoff games than home teams during certain cycles. The Astros’ 2019 World Series loss provides a stark example of the fluctuating effect of home field advantage. In that series, the road team won every game.

In the end, my only advice to the Astros is forget what I just wrote, eliminate distractions when you are at home, and play loose and without pressure in your home ballpark.