## Home Field Advantage and Our New Game Odds

This morning, David Appelman rolled out our site’s newest feature: Game Odds. Essentially, this tool takes our Depth Chart forecasts and applies them to every match-up, and then takes it a step further by calculating the odds based on that day’s actual line-up and starting pitcher, once they are known. Using a few mathematical tools, we use these inputs to calculate an expected odds of each team winning that particular game, so we can beyond things like “the Red Sox are better than the Orioles” and see that, when it’s Ubaldo Jimenez versus John Lackey and the game takes place in Baltimore, the Orioles are actually very slight favorites. When the line-ups come out and replace the depth charts — which still give fractional playing time to injured guys like Shane Victorino — the needle will probably move even further towards the Orioles.

This is the kind of result that makes these numbers interesting and useful, because before seeing them, I probably would have assumed that the Red Sox would be favored tonight. After all, our projections have the Red Sox as a schedule-neutral 87 win team, with the Orioles as a schedule-neutral 78 win team. That’s a pretty decent sized gap, and it doesn’t feel like the difference between Jimenez and Lackey should really push the game towards the Orioles all that much. In fact, our depth chart forecasts have Lackey as a slightly better pitcher than Jimenez, so what’s the deal with the Game Odds suggesting that Baltimore is a 50.2% favorite before the line-ups get posted?

The short answer: it’s home field advantage. While we’re all pretty familiar with the power of home field/court advantage in football or basketball, the spread between the home and road team in baseball is not talked about with much frequency. And that’s because it just doesn’t matter as much. In the NBA, the home team wins roughly 60% of all contests, and the roar of the crowd in an enclosed arena gives a sound track to momentous fast breaks and thunderous dunks. In the NFL, the home team wins about 57% of the time, and it’s easy to see the effect of a crowd when a quarterback has to call time out because his teammates couldn’t hear the play call over the roar of the stadium.

In MLB, though, the home team has historically won only about 54% of the time. There is crowd noise in baseball, but it is usually limited to reactions to a play, not the time when the opponent is actually trying to actively make decisions or communicate with each other. The Pirates distractive chants towards Johnny Cueto in the Wild Card game last year were notable mostly because of how unique they were for MLB, showing how we’re not really used to players on the field having to drown out crowd noise in order to concentrate on the task at hand.

So I don’t think about home field advantage as much in baseball as I do in other sports. Traditionally, if I was looking to pick a winner in a given game, I’d look at the strength of the team, the starting pitcher, and maybe see if either team was missing a star player or not, and then call it a day. Sure, the location of the game mattered a little, but a 54/46 split just isn’t that big of a deal, right?

Well, it both is and it isn’t. Baseball is a game where the difference between a good team and a bad team is simply the culmination of a million tiny advantages adding up over six months of time. A 54/46 split is pretty close to coin flip odds, but over the course of a full season, a team that wins 54% of their games will finish 87-75 and be a playoff contender. Four percent sounds like a small number, but over 162 games, it’s a six win swing. In other words, home field advantage in MLB is akin to swapping out a replacement level player for Miguel Cabrera that day.

I’m pretty sure we’d all acknowledge that, even on a neutral site, the O’s would have a pretty decent chance of beating the Red Sox if they got to swap David Lough for Miguel Cabrera tonight. And because Lough isn’t a replacement level player, the home field advantage gap is probably even a little bit larger than the Lough/Cabrera difference.

So, when you look at the Game Odds for tonight’s games and see that the Padres are favored over the Dodgers, keep in mind where the game is being played. It matters, even if it matters less than it does in other sports. A 54/46 advantage for the home team might not sound like a lot, but in reality, there’s no single variable in baseball that is much larger than that. Baseball is about collecting small advantages and taking advantage of them. Home Field is a small advantage in a game decided by small advantages.

For me, the initial lesson to seeing these Game Odds forecasts was to realize I’d been underrating the importance of home field advantage in MLB. I look forward to these tools teaching me even more things as I take a look at them on a daily basis throughout the season.

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Dave is a co-founder of USSMariner.com and contributes to the Wall Street Journal.

### 25 Responses to “Home Field Advantage and Our New Game Odds”

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1. LK says:

So…the fact that the ASG decides WS home field…

• AK7007 says:

Should actually encourage players to care. Or is unfair. Or maybe it doesn’t matter at all!

• Eric R says:

Series that end in four or six games have equal home and road games for both teams, so HFA for the World Series is only really an advantage if there are more seven game series than five game.

2011 7
2010 5
2008 5
2006 5
2002 7
2001 7
2000 5
1997 7
… in the Wild Card era, dead even, 21% of World Series were 7-games and 21% were 5-games..

In the divisional play era; 40% of series were 7 games and only 24% were 5-games.

In the 25 years before that; 60% were 7-game and 8% were 5-games.

Looks like awarding home field based on some kind of merit made more sense before the play-off system was added…

2. ALEastbound says:

Geez I had my gambling problem under control…

#### +14

• Pete Rose says:

Me too

#### +12

3. rcb says:

Along these lines, I would love to see some SP performance data for the first game in a road series vs all other games. I came to feel like that circumstance represented a “small disadvantage” worth factoring in, even over other road starts, last year but could find nothing to support or shoot it down.

4. PXF says:

How would you go about determining how much of that 54% home field advantage is due to the simple fact that the home team bats last? It would be cool if we could know how much to attribute to that fact, and then also look at park factors to see how well the home team is built to take advantage of its park. Then the remainder would be some combination of crowd impact and randomness.

Related comment: I’ve often wondered if visiting teams that LOSE a high percentage of games in the top of the 9th inning have an advantage in succeeding games (or maybe just immediately succeeding games), insofar as the pitchers have saved themselves three outs of wear and tear. Of course, if a manager factors his knowledge of workload into how he deploys his pitchers in succeeding games, this might not have a huge effect.

• Book_Worm says:

If you look at Win Expectancy charts in Tango’s The Book, the home team definitely has a growing probability of winning as the game goes on, all other things being equal. If a game is tied, the Win Expectancy for each team is always 50% at the top of the inning, regardless of the inning. If the game remains tied to start the bottom of an inning, then the home team gets a bump in each successive inning that they come up to bat with the game tied.

• Max says:

That’s just because they have one more at-bat to score than the away team. And THAT is just because they successfully kept the away team from scoring in the previous half-inning.

• Book_Worm says:

Yeah, exactly. I was just pointing out that what PFX was asking in his first sentence was true: There is an advantage to batting last, and that advantage grows by the inning.

• Catoblepas says:

no I don’t think there is, I think you’re interpreting the WE wrong. what Max was trying to say (i believe) is that bump in WE isn’t coming from batting last, it’s coming from having just held the opposing team scoreless for another inning. there might be an advantage, but it isn’t one we see in the WE tables.

• Tactical Bear says:

There is a sizeable advantage is hitting last as the home team. Strategic decisions are easier to make when objectives are more clearly known. If the game is tied in the bottom of the ninth, playing to maximize the chances of scoring a single run is optimal, for example. But this cuts both ways! Defensive strategies are just as effective when the visiting team employs them! They have access to the same information, and counterplan accordingly.

That being said, HFA is an odd duck. Things like BABIP, LD ISO, and HR/FB ratio (to choose just a few) all favor the home team. A lot of this can be theoretically tracked back to a bias in balls and strikes, but it’s unlikely ALL of it can. There are theories abound, and BPRO wrote a great five part series in 2009 that everyone should read, but HFA has always struck me as one of the most complicated and fascinating interactions in all of sports

5. dixie_flyer says:

a cursory glance tells me that your odds seem to be quite close to today’s vegas odds

6. B N says:

Does this take into account the issue that home field advantage is not evenly distributed? I can’t imagine the Orioles have much “noise” home field advantage against the Red Sox, at least for the last few years, considering it would often have so many Red Sox fans as to be called “Fenway South.” Familiarity, due to being divisional opponents, would also seem to reduce home field advantage impact in this case. So, at that point, you’re largely talking about advantage due to a club designing its team for the park. I’m not sure if Camden Yards has much of that, considering it seems to be a pretty evenly-balanced park.

• Baltar says:

There are lots of things that make a difference between being at home and being on the road, e.g. getting to sleep in your own bed the night before the game. I’m not sure that crowd noise is the main factor, and I am sure that is not as big a factor as Dave indicates.

7. Lex Logan says:

I can’t figure out what menu this would fall under. Fangraphs seems to roll out a lot of cool stuff that isn’t listed or at least isn’t obvious in the menus.

8. WithoutTout says:

Is there anyway that someone could post the formula(s) or work out an example for exactly how Fangraphs calculates the game odds?

9. pft says:

Red Sox have always pounded Jiminez. It will be a blow out. The odds calculator must be dealing with incomplete information.

10. Max says:

The one thing you’re missing here is that home field advantage does not come exclusively from crowd noise. The main factor in home field advantage is that the referees/umpires will subconsciously slightly favor the home team. As human beings we all want to be accepted and while umpires never do it intentionally, they are more likely to call strike three when they know in the back of their mind that they will receive thunderous applause from the crowd.

• pft says:

That may be part of it, but not having to travel and live in a hotel and constructing a team for the home park and secret corridors that allow you to listen in on the away teams meetings (LOL) is part of it too

I also think players may party a bit harder on the road away from wives and girl friends

11. I’ve never understood why basketball has a home team advantage. The court is the same size everywhere and the noise should not interrupt play calls like it does in football. I’m actually surprised that the home team advantage is not larger in baseball. Field dimensions/conditions vary greatly and teams are able to construct rosters that fit their own ballpark in ways that you simply cannot do in other sports. There is probably also something to be said for always getting to bat last.

If I remember correctly the conclusion in Scorecasting, the only factor in home field advantage that had any significant effect was the home crowd influencing the calls made by the referees/umpires.

12. Tim Donaghy says:

Home court advantage in basketball is predominantly due to the social pressure on the referees posed by a crowd favorable to the home team.

13. MrKnowNothing says:

Basketball and football and hockey are games that can thrive on emotion. We’ve seen running backs seemingly carry five defensive linemen on their backs for an extra few yards. And hearing the crowd roar may give a player just a tiny boost of adrenaline that lets them drive to the basket a little harder.

By contrast, baseball is a game that sees a person succeed when they remove emotion. The mechanics of hitting and pitching are so finely tuned and depend so much on near perfect repetition that being able to NOT get caught up in a moment is a positive.

14. conciousness says:

in my opinion another factor in homefield advantage has to do with the fans and what they are hoping for. there is a study out there that shows when a big group of ppl meditate towards peace that it reduces the cities crime rate…it is all about the collective concsiouness…the place where all thoughts go. therefore it is my opinion that when a big group of ppl are rooting for a certain team, that team has a clearer mind…compared to being rooted against, the opposing team will not be able to attain the focus that is neccessary and they will have more of a cloudy mind…they will be at a disadvantage…..there is evidence to back up this kind of thing. the world is a magical place afterall