May 4, 2012
The BP Wayback Machine
While looking toward the future with our comprehensive slate of current content, we'd also like to recognize our rich past by drawing upon our extensive (and mostly free) online archive of work dating back to 1997. In an effort to highlight the best of what's gone before, we'll be bringing you a weekly blast from BP's past, introducing or re-introducing you to some of the most informative and entertaining authors who have passed through our virtual halls. If you have fond recollections of a BP piece that you'd like to nominate for re-exposure to a wider audience, send us your suggestion.
What is it about Tropicana Field that makes the Rays so successful at home? Nate looked at the origins of home-field advantage and made some interesting discoveries about domes in the article reproduced below, which originally ran as a "Lies, Damned Lies" column on June 29, 2008
Home-field advantage is making a little bit of a comeback this year, with the home team thus far having won 56.2 percent of major league baseball games. This is actually down a few ticks from where it was several weeks ago; at the beginning of June, home teams had won almost 58 percent of their games. Nevertheless, this is quite high by the standards of recent history. Prior to World War II (when travel was more burdensome and road trips much longer), home-field advantage was more profound in baseball, but since then it has been exceptionally stable, with the home team winning about 54 percent of games each season. So, is there something systematic that is causing the home-field numbers to increase this year? Or has it just been some kind of statistical fluke?
To address this question, we first need to consider why home-field advantage exists in the first place. In baseball, the home team has a couple of built-in tactical advantages: in the National League, for example, by batting last it can pinch-hit for the pitcher while getting one extra inning out of him. Regardless of league, the home team knows exactly how many runs it needs to play for, which making ninth-inning strategy easier.
However, there are other elements that differ from park to park. Some parks favor hitters, and some favor pitchers. Some parks are asymmetrical-favoring batters that hit from a certain side of the plate-whereas others treat all hitters equally. If teams are becoming more aware of such differences and more aware of how to exploit them, that could explain the uptick in home winning percentage.
Let's examine six or seven variables that might conceivably be related to home-field advantage, rating each major league ballpark from 1 (lowest) to 5 (highest) based on a somewhat subjective assessment of those categories.
Based on a combination of objective (the lefty/righty splits in my park factor databases) and subjective factors, this is how we might classify the parks from most asymmetrical to least. Some parks behave counterintuitively. For example, U.S. Cellular Field is very nearly symmetrical, but for whatever reason-perhaps the prevailing wind conditions in the area-it has tended to be much friendlier toward left-handed hitters. That said, here are my ratings for how much the parks "lean":
5: Boston, Houston, Pittsburgh, San Francisco
5 (most favors hitters): Colorado
Fences and Caroms
5: Colorado (altitude), San Francisco (wind/cold), Texas (heat)
Yes: Arizona (retractable), Houston (retractable), Milwaukee (retractable), Minnesota, Seattle (retractable), Tampa Bay, Toronto (retractable)
Attendance and Atmosphere
5: Boston, Chicago Cubs, LA Dodgers, NY Yankees
5: Florida, San Diego, Seattle, Tampa Bay
Going back to the larger problem, which teams have actually had the largest home-field advantage of late? This can be calculated simply by subtracting the team's winning percentage on the road from their winning percentage at home in all games since 2004. For the Cardinals, I use only their numbers since they moved into their new ballpark in 2006, and I exclude the Nationals entirely since they've played only half a season in their new facility.
Table 1: Home and Road Winning Percentages, 2004-2008
Team HomeW% RoadW% Difference TBA .516 .340 .177 MIL .569 .394 .175 BOS .655 .508 .147 COL .530 .385 .146 TOR .558 .419 .139 PIT .500 .371 .129 SLN .572 .450 .122 HOU .572 .455 .117 SEA .507 .391 .116 TEX .556 .443 .113 NYA .645 .537 .107 ATL .585 .481 .104 MIN .586 .494 .092 CIN .508 .418 .090 LAN .554 .466 .088 KCA .428 .346 .082 OAK .575 .501 .073 CHN .549 .479 .070 CHA .568 .499 .070 CLE .558 .496 .062 ARI .490 .429 .062 NYN .548 .492 .057 FLO .515 .463 .052 SDN .541 .496 .045 DET .523 .479 .044 SFN .496 .460 .036 LAA .591 .559 .031 BAL .478 .448 .029 PHI .544 .530 .014
The kings of home-field advantage over the past several seasons have been the Rays and the Brewers, each of which have about an 18-point gap between their home and road winning percentage. Whether this is a result of their playing particularly well at home or particularly poorly on the road, I don't know; if you're looking for the team that has actually won the most home games, that would be the Red Sox. It's also funny to see the Phillies at the bottom of the list when half the time their fans seem to be rooting against them.
Do we find any relationships between these numbers and the variables that we described before?It turns out that only one of them has a statistically significant relationship with the home/road win percentage gap, and that is playing in a dome. Arizona, Houston, Milwaukee, Minnesota, Seattle, Tampa Bay, and Toronto have combined for a 54.3 percent winning percentage at home since 2004 versus 41.7 percent on the road, a difference of 12.6 points. By contrast, the other (non-dome) teams have had a gap of 7.7 points between their home and road performances.
The question I don't yet have an answer for is the 'why'. Could it be, as I hypothesized before, that playing in a dome may provide some advantages in terms of outfield defense? Might it be that playing baseball under a roof is a miserable experience that demeans the human condition and tends to depress the visiting club?
For the time being, I'll leave you with the stathead's version of the dog-ate-my-homework excuse: this is a direction for further research which I'll revisit again in a couple of weeks. It does not appear, however, that the uptick in home-field advantage this year has anything to do with teams taking better strategic advantage of their home facilities, as both teams that play in bland ballparks like Atlanta and idiosyncratic ones like Boston have had quite strong home/road splits thus far this year.