I found myself browsing the MLB standings Monday morning. My team is way out of the race, and I'd been thinking about the trade deadline for much of the previous week, so to some degree I kind of lost track of who was where. This was my refresher.
There wasn't a lot that took me by surprise, meaning that either little has changed, or I knew more than I thought. All three AL divisions are close, with the Yankees way out in front of the Wild Card. Two of the NL divisions are close, with the Braves well out in front of the Wild Card. I focused on the NL Central, since that's been a hot race, but we're beginning to see some separation, with gaps of 2.5, 4.5, and 6.5 games between the Brewers and their pursuers.
But while I was looking at the NL Central, my eyes drifted over and caught the home/road records. That's where I noticed the following:
Brewers, home: 39-14
Brewers, road: 21-35
That's a difference of 36 percentage points. The league average is a difference of nine or ten percentage points. Clearly, the Brewers have played way better within Miller Park this season than they have without.
One thing led to another, and before long I was staring at a spreadsheet of home/road data dating back to 2002. This gives me nearly ten years of information, and I was curious to see which teams have gotten the biggest and smallest boosts from playing at home. Have the Brewers been a fluke? Is there something more to this? What about everybody else?
Following is the complete table. The teams are sorted by the difference between their home winning percentage and their overall winning percentage.
Now, an assortment of thoughts on this data:
(1) Montreal and Washington get asterisks for what I should hope are obvious reasons - Montreal includes only three years of data, while Washington includes seven. The smaller the sample size, the lesser the meaning.
(2) One figures that home-field advantage would be strongly influenced by the ballpark. A number of these teams have changed ballparks within the last ten years, including the Yankees, White Sox, Twins, Phillies, Mets, Nationals, Cardinals, Reds, and Padres. In some cases it shouldn't make much difference, while in other cases it could.
(3) A big boost from playing at home isn't necessarily a good thing. The Phillies rank last above, but they're fifth in overall winning percentage. The Angels are 28th and 3rd. The Pirates are 6th and 30th. Building a roster that can win at home is nice, but you have to be able to win away, too.
(4) We can't assume that home-field advantage is static. Not only is there a lot of noise in the data; the information is always changing. Front offices will, in theory, construct their rosters to fit the home ballpark. As they learn more about the home ballpark, the roster should reflect it. Park factors are still kind of hard to figure out.
(5) This is evidence against the idea that crowd size and volume matter. At the bottom, we find the Phillies and Cubs, who have routinely drawn large, raucous crowds. Near the top, we find the Rays (and the Expos), who have routinely drawn several family members and curious passersby.
(6) As we'd expect, there are hints that more extreme ballparks are more favorable towards their regular occupants. Coors Field is insane. The Expos had turf and a dome. The Rays have turf and a dome. The Twins, for a while, had turf and a dome. Houston's weird, and Texas is kind of weird, and so on and so forth. This makes sense - the quirkier the ballpark, the bigger the effect of targeted roster construction, and the bigger the advantage of player familiarity. But this model isn't perfect.
(7) Haha Red Sox, you're unexceptional.