Of the four major sports, MLB home teams have the lowest win percentage, regular season or postseason. The 54% win percentage implies that the crowd, umpire bias, ability to bat last and other home factors only swing the result in one out of every twelve or so games.
Home teams in the NBA and NFL both win at least five percent more games in the posteason, as opposed to the NHL and MLB, which don't see any "bump" in the playoffs.
When diving a little deeper into the MLB numbers, I noticed that home-field advantage is even less of a factor earlier in the postseason.
I split the postseason history into four separate time periods based on when Major League Baseball added a new round (or second Wild Card).
Since the American League and National League split into separate Divisions in 1969, home teams have won 60% of World Series games but only 52% of LDS games. The sample size is almost meaningless, but road teams have actually won seven of the ten Wild Card games played since 2012.
If you go back to 1995, after the strike and realignment, teams with home-field advantage have won exactly 50% of LDS series (44-44). Since 1998, when MLB adapted the 2-2-1 format, teams with home-field advantage have actually lost more series than they have won in the LDS (35-37).
Home-field advantage seems to be the most valuable in the World Series, as teams with home-field advantage have won 59% of those series since 1925.
Last season, the Cubs pulled out a road win in the 39th "winner-take-all" game in World Series history. Home teams in World Series "winner-take-all" games now own a record of 19-19, but they did win nine of ten prior to last season. (Bumgarner in Kansas City is the exception.)
If you look at the home/road splits for the ten 2017 MLB playoff teams, you will notice that four of the ten actually own better road records, backing up the theory that home field doesn't matter that much in baseball.
However, exceptions do exist for certain teams as a result of other variables such as team experience, ballpark dimensions, weather, sightlines, etc. For example, it shouldn't be a surprise that the Rockies and Diamondbacks both have better home records, since their slugging lineups are built for their respective parks.
Additionally, for a number of potential reasons, certain pitchers perform significantly different in certain parks.
Eleven of the seventeen listed AL starters above (I excluded mid-season acquisitions Justin Verlander and Sonny Gray) actually have better road ERAs, but Berrios and Tanaka really struggle on the road, while Kluber and Keuchel generally just dominate even more in their home ballparks.
Similarly, ten of the seventeen listed NL starters above (excluding Yu Darvish, Jose Quintana, and Tyler Anderson) have better ERAs on the road. As a result of Rich Hill's favorable home splits, the Dodgers actually decided to push Darvish to Game 3 on the road so Hill can pitch in Los Angeles.
Having reviewed all of the above data, you would assume that home favorites in the postseason, especially in earlier rounds, are overvalued. Using the valuable tools on BetLabs, I ran a return analysis on betting road MLB underdogs in the MLB playoffs.
If you bet $100 on every road MLB underdog of +120 or better since 2006, you would have won ~$2500 (12.7% ROI) with a record of 90-107 (45.7%).
If you are looking at the game tonight, I think the Yankees are indeed overvalued at home. I think it is Twins and the under 7.5 or nothing tonight, but I ultimately decided to stay away.
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