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October 6, 2012

BP Unfiltered

Playoffs and Home-Field Advantage

by Sam Miller

Since 1995, home teams have won 53.936 percent of baseball games played in the regular season. Considering that a large portion of home field advantage is, by conventional wisdom, attributed to the effects of home-crowd fans (either on the players, or, more likely, on the umpires), we might reasonably expect the home team to get an even bigger boost during October, when the crowds are bigger, perhaps more partisan, and generally more bananas. 

Since 1995, home teams have won 53.986 percent of baseball games played in the postseason. This number is somewhat less reliable because the sample size (552 games) is so much smaller, but if it we conceded it is an accurate representation of the postseason home-field advantage, it would mean that the home teams in the past 18 years of playoffs have won a total of 0.27 more games than they would have won in a regular-season environment. Which is to say, zero games. So, identical. 

Surprising and interesting, is all. 

(Update: Complicating this is also the fact that "better" teams would probably get to play a few extra home games in October, because of how the playoff rules work. So by a small amount, the home team should be, on average, a bit better than the visiting team in October; in the regular season, the teams are, on average, equal.) 

Sam Miller is an author of Baseball Prospectus. 
Click here to see Sam's other articles. You can contact Sam by clicking here

Related Content:  Playoffs,  Home Field Advantage

12 comments have been left for this article. (Click to hide comments)

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Have to say, I would have to think the home-team advantage is way more attributable to getting last ups, as opposed to any crowd factor. It's a big advantage late in the game, and even more so in extra innings, to be able to end the game in your at-bat but always to be able to match any visiting-teams runs. Apart from the better team getting home-field advantage.

Oct 06, 2012 22:13 PM
rating: 2
Richard Bergstrom

I agree. A visiting team needs to win a game in 9 innings, a home team has to win it in 8.5 innings. Also a 0.27 edge is still pretty significant, especially if a team that goes to the World Series would play anywhere from 10 to 19 games.

Oct 07, 2012 23:10 PM
rating: 0

Sam says that the home team has won .27 more games, NOT per series, NOR per season, but rather out of 552 games over an 18 year period.

If my stubby little fingers pushed the right buttons on the calculator, that 53.986 post season winning percentage comes out to a record of 298-254.

A 59.936 regular season winning percentage would result in a record of 297.73-253.27.

As a team can't actually win .73 games, it rounds up, and comes out perfectly as predicted by the regular season winning percentage.

That is what is commonly known as a rounding error. It is not "still pretty significant" at all.

Oct 08, 2012 23:11 PM
rating: 0
Richard Bergstrom

I did use the 0.27 wrong so thank you for correcting me.

I think part of what Sam is also saying is that the home field advantage during the playoffs specifically should be amplified when it is not. In general, though, he seems to suggest a home field advantage exists in general. It just doesn't get much of a playoff bump.

Oct 09, 2012 10:02 AM
rating: 0

The mechanical advantage of the ordering (visitors bat first) is unclear. It influences player substitution, but each side gets an advantage:

1) The visitor can choose pitchers and defenders based on the score. With a one-run lead, they can put in their best pitcher/defense and aggressively substitute based on match-ups. With a tie, they can more strongly consider the impact on future innings.

2) If the visiting team took a lead in the top half, the home team can aggressively use bench players to pinch hit or run, because they know they have to score or lose. If its tied, they know they have to think about additional innings.

Short version: Does 'bats last' necessarily overcome 'pitches/defends last'? What percentage of extra-inning games are won by the home team? Bigger or smaller than the 54% generic home-field advantage?

Oct 09, 2012 08:37 AM
rating: 0

Shhh, don't tell this to the announcers.

Oct 07, 2012 09:40 AM
rating: 0

I always found it curious as baseball is the one major sport with a home-field advantage built into the game (as frampton identified), that there is far less hpme field advantage than in football, basketball or hockey. Is there some counterveling force?

In the other sports, emotion and ramping up intensity is almost always a goiod thing. In baseball, it is almost always counter-productive. Maybe the heightened home atmosphere degrades performance? Just a thought.

Oct 07, 2012 15:56 PM
rating: 0

Even more that getting to bat last, it seems like the home team has an advantage in their familiarity with the field of play and that the roster might have been built with the ballpark dimensions in mind.

Oct 07, 2012 17:34 PM
rating: 0
Richard Bergstrom

Groundskeepers also can sculpt the field to play up to their team's strengths, such as height of infield grass, dampness of infield dirt, etc.

Oct 07, 2012 23:11 PM
rating: 0

Travel also matters. It would be interesting to look at regular-season home-field advantage in the first series of a homestand (where the home team has also traveled prior to the game), vs. home-field advantage in the second or later series.

A dedicated analyst could also look at home-field advantage as a function of:

1) Rigor of travel (miles as the crow flies is probably sufficient as a first guess, but some stadiums are hard to get to even after you've landed)
2) Number of days since last travel.
3) Era (Ty Cobb didn't have a charter plane waiting for him.)
4) Number of time zones crossed.

I'd expect that all four are more significant than the +0.27 wins per 552 games of extra postseason "excitement" advantage. #1/#4 are well-documented in the NFL, where east-coast teams do worse than expected when playing night games on the west coast.

Oct 09, 2012 08:49 AM
rating: 0

Hockey may have the strongest inherent home advantage because during stoppages, the road team has to put their players on the ice first, and the home team can react accordingly. The road team also has to put their stick down first in faceoffs.

Sam links to a review of the book "Scorecasting," which looks into things like this. It attributes HFA to refs being biased to the home team because of the crowd, but that review is skeptical.

Is it possible the amount of scoring has anything to do with it? As far as postseason goes, it seems basketball's the one sport where the better teams usually win series. Baseball and hockey are low-scoring, and their playoffs are a crapshoot (a few years ago, the 5-8 seeds won the first round in the west). So wouldn't luck seem to be a bigger factor when scores are lower? I have no idea if this pertains to soccer playoffs, but they don't play series do they?

Oct 07, 2012 21:16 PM
rating: 2
Michael Bodell

Soccer often plays home and away series and has some of the same issue.

From a statistical modeling perspective if the scoring is lower/less frequent than the worse team can win more for reasons similar to the small sample size.

If team A scores a run on average every 0.200 of a game and team B scores a run on average every 0.250 of a game then team A on average scores 5 runs and team B 4 runs and A is a favorite over B. If you imagine that run scoring is a Poisson process with that rate and then simulate games (count how many run events before 1, and if tied the next scoring event wins) you'll see that A will win more of the games, but B will win a decent chunk. If you change that to the same ratio but many more events (so A scores every 0.02 games and B scores every 0.025 games) you have the same ratio of 5:4 but now A scores 50 runs to 40 runs on average and if you run the same sort of simulation A will win many more times.

Scoring in baseball isn't really a Poisson process, since scoring events are linked and correlated, but the model above is a good first order approximation to why teams that are better in sports that are high scoring might well be much more likely to win than "equally better" teams in sports that are low scoring.

Oct 08, 2012 15:25 PM
rating: 1
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