On the second-to-last day of the season, the Tampa Bay Rays used Andy Sonnanstine for just his fourth start of 2010.  In their season finale, the New York Yankees went with Dustin Moseley, who made his ninth start and finished the year with an ERA just under 5.00.  Jason Bartlett, Derek Jeter, Nick Swisher are among the healthy Yankees and Rays players held out of starting lineups in the final series of the year.  Evan Longoria did not play the entire final week of the season because of a minor quad injury.

You wouldn't know it from the way they went about their business, but these teams were battling for both the AL East crown and for the best record in the American League.  The Rays wound up winning both due to their unparalleled depth and inferior opponent in the Royals, but the alarming development is that neither team tried their best to get home field advantage.  This is surprising, since home field advantage has never been more important in Major League Baseball.

It has never quite made sense that the home team in baseball wins less than 55% of the time historically.  NFL teams win about 60% of their games while NBA teams win nearly 70% of theirs, but they don't have the inherent advantage of getting the last at-bat or playing in idiosyncratic stadiums.  They also have more time off for travel than MLB teams do.  Logically, MLB should have the biggest homefield advantage of the three sports, but historically, they have had the smallest by far.

For equally perplexing reasons, however, the homefield advantage in Major League Baseball is beginning to increase.  Home teams won a whopping 55.9% of their games in 2010, the highest winning percentage since home teams won 57.3% of their games in 1978.  We do see spikes in the data for stats like this.  For instance, two years after teams won 55.2% of their home games in 1992 (the highest such winning percentage in a 29-year span), they won just 51.7% of their home games (the lowest such percentage I could find), no doubt due in part to a smaller sample size created by the 1994 strike.  But this year's increase is part of a trend;  in the past five seasons, home teams have had a .550 winning percentage compared to a .538 winning percentage the previous five years.  Since we are talking about sample sizes in thousands of games, this is a substantial effect, the cause of which is quite mysterious.   

The most extreme instances of the hometown advantage were seen in Pittsburgh and Detroit. The Buccos were a half game under .500 at home, but won just 17 games away from PNC all year.  There are several jagged features to the outfield fence there, which creates interesting caroms that the home outfielders are more used to, but that hardly explains a 23-win differential.  Pittsburgh also ranked 27th in home attendance, so it's hard to believe that Pirates players were driven to succeed by thunderous fan support.  The Tigers tied the Yankees for the second-best home record in the American League at 52-29, but their palindromic road record of 29-52 tied the road marks of the lowly Orioles and Royals.  Detroit also had a 16-win differential between their home and road win totals last year, and their inability to win on the road ultimately cost them a one-game playoff with the Twins for the AL Central title.  Why Comerica Park should suddenly provide this kind of advantage the past two seasons is anyone's guess.

The two other teams to have a 20-plus home/road win differential in 2010 were the Braves and the Rockies, each coming in at +21.  As of September 1st, the Braves were in line for the homefield advantage throughout the postseason, and would have to been considered the favorites to win it all given the fact that they finished with the most home wins in baseball.  The Phillies' fantastic September run has instead relegated the Braves to Wild Card afterthoughts in the postseason.

Interestingly, the Braves actually finished six games better on the road than at home last season.  The Rockies, on the other hand,  have been used to having a homefield advantage, although normally not as extreme of an advantage as they enjoyed this season.  Happily, it is one of the few instances of homefield advantage in baseball that actually yields a satisfactory explanation.

No, I'm not talking about the allegations that the Rockies are misusing their humidor to give themselves an advantage.  Coors Field had been an advantage long before the humidor was installed, as the playing conditions there are completely unique in Major League Baseball.  The humidor was first installed in 2002, but they began storing baseballs in there much longer during the 2006 season.  Amusingly, people first began to whisper about the humidor being used underhandedly in that 2006 season even though their home field advantage was slightly less than it was in 2005 and far less than it was in 2002 and 2003.

This season, the whispered outrage at least has some statistical basis, as the Rockies enjoyed their greatest home field advantage since 2003.  But really... it looks just like a normal statistical spike to me.  If you're going to accuse the Rockies of using different baseballs when they pitch than when they hit, shouldn't you also make accusations towards the Pirates, Tigers, and Braves, all team that haven't exhibited a consistent homefield advantage in their team histories?

What the revamped humidor usage did, actually, was not so much to give Colorado more of an advantage at home (they already had that).  Rather, it put them at less of a disadvantage on the road.  Pre-humidor, Rockies hitters would go on a road trip not having seen a real major league breaking ball for a week or more.  Rockies pitchers would struggle with their command, seeing their pitches behave completely differently in home starts than in road starts.  So although the Rockies have improved their average home records by nearly six wins from the '02-'05 period to the '06-'10 period (and keep in mind they had an extra win in '07 due to Game 163), they have improved their average road records by more than eight.

Coors Field is still the best hitter's park in the majors, but at least it is only head above the others rather than head, shoulder, and torso above as it was pre-humidor.  As for the Rockies performing much better in Coors than on the road, that does not appear likely to ever change, whether a frustrated NL West rival blows up the humidor there or not.

Anyway, getting back to things that don't make sense... how about those Minnesota Twins?  Like the Rockies, they were a team that consistently performed better at home due to their unique ballpark.  But the Metrodome is gone and replaced with an outdoor stadium that is mostly ordinary, although Target Field did suppress home run totals to a surprising degree in its inaugural season.  All the Twins have done in 2010 is post the best home record in the American League despite the loss of their supposed home field advantage.

With the demolition of the Metrodome, the Rays now have the only full-time domed stadium in the American League and is only one of two to use artificial turf.  That translates to a big time homefield advantage, right?  Not so much.  With only two ore wins at home than on the road, Tampa tied the White Sox for deriving the least advantage for their home games among AL teams.  Those same White Sox had 18 more home wins than road wins in 2008, or 19 if you count their coin-flip victory over the Twins in game 163.

But even if the Rays don't seem to derive much benefit from playing at home themselves, shouldn't they have played a little harder in the final week to make sure that the other playoff teams receive the detriment of playing on the road?  The Rangers were just a 39-43 road team this year, while the Twins went 41-40 and the Yankees 43-38.  All's well that ends well, but I'd have put a little more urgency in my efforts to host Texas rather than travel to Minnesota for the ALDS.

As for the Yankees, they send their 43-38 road record against Minnesota's 53-28 home record.  Vegas still has the Yankees heavily favored to win that series, but it seems to me that the Bronx Bombers would be favored even more if they were hosting Texas.  Not only are the Twins a better team than the Rangers, but home field advantage means more than it ever has before in Major League Baseball.