How Big Is Home Field Advantage? Part Two (by JonathanF)

So what does the home field advantage in baseball look like? In my database of almost exactly 200,000 baseball games which didn’t end in ties, the home team won 54.7 percent. But road teams did really badly in the early days of baseball. Before 1900, the home team won 59.1 percent. Post WWII, only one year had an advantage over 57 percent: 1978.

For simplicity, I’m going to assume baseball started in 1966. Of course, for many of us, that’s the year baseball actually started. That’s arbitrary, of course, and I’m not saying that the data couldn’t be mined to make interesting cross-era comparisons. But since I have a prior supposition that travel is important, I want to look at 162 game seasons played on both coasts and north and south with travel largely by airplane. If I go too much farther back all of those are in doubt.

That still leaves us with almost 100,000 games (97,632 to be precise). I should note that while the 2012 season is now available, it wasn’t when I made this database, but I’m going to fix that before the next posting. So for now I’m covering 1966-2011. The aggregate home winning percentage in this period: 53.9 percent.

The following figure shows the home advantage:

Now, a word about variance. In a typical year there are around 2,400 games. Suppose the home team has a 54 percent chance of winning each of them. This is like flipping a coin with a slight bias towards heads 2,400 times and seeing how often it comes up heads. We certainly wouldn’t expect to see 0.54*2400=1,296 every time. Sometimes we would observe more, sometimes less. That doesn’t mean that the true underlying tendency is really moving around in any way, just that the randomness of the process yields different results.

In fact, the post-1966 splits, season by season, look exactly how you’d expect them to look if the underlying probability were constant at about 54 percent. There are two outliers that are a little surprising (1978 is quite a bit too high and 1969 is a little too low) but you’d expect a couple of surprising runs in 45 years of looking. So I’m going to argue that everything we see at an aggregate level away from 54 percent is just noise. Despite the natural human tendency to see a trend, for example, in 2004-2010 it almost surely isn’t really there.

In the charts above, I’ve put annual 95 percent confidence limits in to show just how volatile this data can be even over a season. The shrinking of the limits reflects the fact that more and more games are played, and the two notches reflect the lower number of games played in the strike years.

This puts some real limits on what we’re able to get from this data. For example, one obvious way to get at the question of how big the home field advantage really is to look at games on neutral fields. In that case, the only home field advantage (presumably) results from the last-at-bat strategy. The problem with doing this is that there aren’t many such games.

We had a few played in Tokyo, a few in Puerto Rico, a few where weather caused the team to bat first even though they were in their home stadium (those games would be really really interesting if there were more than a handful of them) and a few other exhibition sorts of games. That said, without thousands of such games, you have no idea whether what you’re seeing is a real effect of “home-ness” or just variance – some lucky coin flips. Any proposed factor that doesn’t show pronounced effect is always just going to look like noise.

With that in mind, I can show you all the first test I did. Many have speculated that travel causes the home field advantage. Since in every other sport, the visiting team usually travels to a home team who is already home, the enervating effects of travel should affect road teams more than home teams in other sports, leading to a home field advantage.

This portion of the home field advantage will be reduced in baseball because of the series effect. Most baseball games are not played by teams that have traveled the day before. This leads me to suspect that the home field advantage should be lower in baseball because the probability of a traveling team being the road team is lower.

Note that of course both teams are in general tired all the time from travel. That shouldn’t affect this hypothesis at all. We only have to assume that: (1) travel yesterday lowers your chance of winning and that (2) it may be countered by the fact, if true, that the other team also traveled yesterday.

So I looked at all the games in which the team played in another city on their previous game and compared it to those games in which they played in the same city. I have begun to look at some wrinkles on this, like how many days it was since your last game and how far you traveled, but let’s ignore this for now.

For home teams, we have 14,000 travel days and 83,632 non-travel days. We find that the probability of winning on a travel day is 54.3 percent, against 53.9 percent on non-travel days.

This difference is nowhere near high enough to reject a simple variance-based result. And even so, the difference isn’t in the direction we had hoped. Now of course a home team in a new city has traveled home, so there could be a degree of elation just in ending a road trip which contributes, in however small a way, to a heightened probability of winning.

For road teams, we have 32,223 travel days and 65,409 non-travel days. (As you’d expect, if most series are 3 games long). Here, at least, the results are in the right direction. On the first game of a series, road teams won 45.9 percent of the time, while in subsequent games, they won 46.1 percent of the time. This could be due to variance as well, but at least the difference is in the direction specified by the hypothesis.

What about the hypothesis that both team traveling eliminates the travel advantage? We get the following percentages of the home team winning:

Both Teams Traveling: Home teams win 54.3 percent (14,000 games)

Road Team Only Traveling: Home teams win 53 percent (18,228 games)

Disappointingly, this once again worked in the wrong direction. Visiting teams who travel in to face a home team who has been sitting at home waiting for them actually do very slightly better than when both teams last played elsewhere. But more importantly, the difference is really tiny against the background of the underlying variance.

Now there’s a lot more things you can do with this, and we might. Some have already proposed looking at the advantage for good teams and bad teams, for distance traveled, and we can take this exploration anywhere people convince me that it would be interesting to go.

So I wanted to show that home field advantage in baseball is attenuated by an attenuated travel cost. My hypothesis appears to be incorrect. That doesn’t mean that travel doesn’t cause the home field advantage in any sport, but the effect surely isn’t one that diminishes over a day of nontravel. That’s what I know so far. Your questions, comments and criticisms are invited.

56 thoughts on “How Big Is Home Field Advantage? Part Two (by JonathanF)”

  1. Jonathan F.,

    Great work.

    A thought on another variable that would be very hard to measure. i believe baseball has a greater problem with “over emotion” than most other sporting events. i think going to “non team” events might help massage this out.

    For example, in professional football, I believe quarterbacks and place kickers are more likely to noticeably underperform from “over emotion.” It is almost impossible for defensive lineman to under perform from “over emotio’ (except for personal foul penalties).

    In baseball, the pitcher’s control has to be exact. The batters plane of swing has to be exact. Trying to “do more” usually results in “doing less.”

    So, I wonder if comparisons to things like golf, archery, shooting sports, or other such might provide insignt.

  2. Really enjoying this. One aspect of travel that I’ve thought worth considering is the the notion of how comparatively restful being at home actually is. A team on the road has a collective itinerary, and gets driven to and from the ballpark from a nearby hotel. And being away from home can mean a respite from mundane distractions. The home team players, meanwhile, might be driving an hour each way, spending time with wife and kids, fixing the kitchen faucet, kicking the neighbors out of the house at the end of the night, or whatever else home life might mean to them.

  3. Loving this series. But as far as methodology goes, shouldn’t you be trying to determine whether teams performance is better at home then on the road? Also, where the home team traveled the day before the game, they should have some lag in performance due to travel, no? it’s not clear to me that it’s being picked up in this study.

    Job 1 in the analysis though has to be to determine the criteria by which we say that one team outplayed another. I know that w-l are probably the easiest stats to access, but may not be the best.
    good work on the series though. loving it.

  4. Sansho1: I’ve always thought about the same thing. I think there are a bunch of issues that go in both directions. I always think that when a team gets home at 3 in the morning, they still have to get from, say, the airport to Alpharetta, while a team that arrives in a road city at 3 in the morning takes a bus directly to a convenient downtown hotel.

    On the other hand, the devil finds work for idle hands, and hands are generally more idle on the road. There might well be differences in performance between bachelors and married/attached guys on the road vs. home, though it’s hard to know which way it might run.

    kruger…. the study directly addresses one of your questions. Home teams which traveled the day before do a tiny bit better than home teams that didn’t…. insignificantly so, but that’s a big blow to my hypothesis. As to team performances, the next installment will say some more about that. (For those getting tired of this, I only have two more installments in mind.) Also, wins and losses are a pretty crude measure, of course, but if the results don’t show up in wins and losses, what’s the point?

    Anyway, the next installment is going to look at home field on a team-by-team basis, and the last installment is going to look at Joey T’s suggestion to try and measure the bats-last effect, as well as summing up. Thanks for everyone’s interest.

  5. @4 — I’m relatively sure there’s sufficient data to conclude that a major league athlete on the road is likely to find plenty of “work” for his idle hands, regardless of his marital or other amorous relationship status at home. cf. Jim Bouton’s “Ball Four” and Chipper Jones’s “divorce and out-of-wedlock child due to relationship w/Hooters waitress.” :P

  6. Apologies if this was addressed in an earlier episode and I didn’t see it, but on the aggregate, does pitching or hitting decline more for away teams, or is it an across-the-board decline (homeOPS-awayOPS [>,<,=] homeOPSallowed-awayOPSallowed]?

  7. @8: This isn’t OPS. It’s just W-L, and at the league level. So We’re just looking at home win probability = 1- road win probability across two conditions: traveling the day before or not. One other control is whether or not the team you faced traveled the day before. In the case of teams traveling before a homestand, the other team aways traveled as well. For road teams, it depends on whether it’s the start of a homestand or the continuation of a homestand. Nothing shows any significant differences. That’s it.

  8. For measuring the strategic advantage of batting last versus any other home field advantage due to travel related effects, etc., you could compare your results to a large, random sample of Little League games.

  9. If anyone is fluent in Spanish, Avilan the Untouchable is very active on Twitter.

    Being old, and new to Twitter, I am amazed at the number of young women who are baseball fans. I had no idea. No wonder they don’t need greenies any longer.

  10. It would be interesting to see if a last at bat effect varies over the decades, as the role of the 9th inning specialist evolved.

  11. JonathanF

    Good work, great chart to look at. I especially like how the strike years show so vividly on the chart.
    But what’s up with 1978?

  12. @16, it’s worse. Perez is sort of like a much worse version of Teheran: eye-popping stuff that he can’t harness. Taijuan Walker is a much better prospect right now. Olt might be a bit better than Franklin, I’m not sure. It’s certainly a competitive offer, but I get why Arizona would opt for the Seattle offer instead.

  13. @17: “What’s up with 1978?”

    Well, I graduated from college that year, so a lot of things were pretty messed up. Only slightly more seriously, 1978 was the year when baseball exhibited a nearly football-like home field advantage. I’m going to look at 1978 (at least in passing) in the last part of the series. But for now, I think it’s just luck. It’s just that streak of flipping coins where you got over 57 percent heads when you were expecting 54. 1968 is almost as odd in the other direction, and we all know how odd the US was in 1968. Now the natural inclination is to ascribe the low home field advantages in 1968 to “The Year of the Pitcher.” The problem with that theory is that 1967, with the mounds at the same heights and almost the same teams was a big homefield year. Again: my guess (at the moment?) Random.

  14. @20, My read is that Wren’s calls are the ones that Towers isn’t returning. Towers wants the Rangers to engage, but they won’t…

    I do think eventually we’ll land Upton.

  15. Yeah. Towers knows that the Braves want Upton, so the best thing he can do right now is try to drive up the price on him. If he has any plausible alternatives then the Braves will have to pay more. But he’s been coming up short in the plausible alternative department.

  16. Simmons could very easily be one of the most valuable SS in the majors in 2013, which would place him high in the running for most valuable players in the majors. I’d like to think that FW knows this.

  17. Also, Simmons is excessively valuable to this team as currently constructed. The rotation features 3 groundball pitchers and the infield defense will have both Uggla and FranCisco at least a couple times a week.

  18. #Phillies announce signing of OF Delmon Young to one-year, $750,000 contract with performance bonuses.
    Ken_Rosenthal(4 minutes ago)

  19. @Buster_ESPN
    The Diamondbacks continue to weigh offers for Justin Upton and Jason Kubel, and they want to deal one of them sooner rather than later.

  20. Nice work, Jon F.

    Doesn’t break my heart to see Delmon Young joining the NL East. But I know one club that doesn’t mind seeing him leave the AL: The NY Yankees. Young has destroyed them in the post-season.

    Simmons is obviously a trade-conversation ender. He ain’t going anywhere. Can’t wait to see him play an entire season.

  21. Thanks for the link.

    Question: “How much s*** did Beachy get after Notre Dame lost?”

    Medlen: “His imaginary gf dumped him… i felt bad so i didnt say anything. :)”

  22. Ruben Amaro seems to have terribly misread all of the bloggers saying that the Phils really need to get Younger.

  23. So I hadn’t realized that Greg Maddux would be the pitching coach for Team USA in the WBC. Awesome. I hope Medlen goes over and says hi. Also, I loved this:

    Have you ever tried to stand in against Kimbrel during BP or spring training? If so, did you make contact?

    No, but I’ve played catch with the guy and he is not fun to play catch with.

  24. @47, I had about ten seconds of joy upon realizing that, but then I realized that Joe Torre is the manager and Kimbrel’s in the ‘pen… :( :( :(

  25. Could a possible explanation for the apparent upward trend in home team performance for the 00’s be in relation to greater offensive output? The easier it is to score runs, the more likley having the final at bat will be decisive. It’s just a thought.

  26. This is really cool.
    In looking at your data, what MLB team has had the biggest unexpected disparity between home and away wins?

    That is, has there ever been an MLB team that approaches the home and road winning percentages of the 2000 New Orleans Saints?

    That team was 7-1 on the road but 3-5 at home.

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