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 the Managing Editor of FanGraphs.


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LK
Guest
LK

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

AK7007
Member
AK7007

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

Eric R
Guest
Eric R

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…

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