Capital Gains
The Nationals and Home Field Advantage

Whenever a team exceeds expectations, analysts race to the keyboards to offer explanations for the success. If a team makes a dramatic turnaround with a similar core of players, as is the case with the 2005 Washington Nationals, the explanations can get pretty gooey and intangible. One of my favorites is the idea of Home Field Advantage. Intuitively, it seems reasonable to say that a team would play better in a familiar environment, with each player sleeping in his own bed, and so forth. However, precious little data explain the effect that a home stadium can have a team’s success. Obviously, the Red Sox are better at Fenway, but how much of that success is attributable to the fans, how much to Theo Epstein for constructing the right team for the park, and how much to the effect of being comfortable at home?

I’m not ready to dive all the way into the intangibles just yet, but I have devised a toy that can help to quantify just how much advantage a team gains from their park by comparing them to themselves away from home. I don’t mean a comparison of how many homeruns, for instance, a team hits at home versus on the road; that’s nothing more than a park factor and says little about an actual home field advantage. Instead, I’m looking at a ratio of ratios: the ratio of home runs hit by a team at home to their opponents’ HRs divided by the ratio of HRs hit by that team on the road to their opponents’. I’ll call it the Home Field Advantage Ratio:

HFAr= HomeH/VisitorH / HomeA/VisitorA. Where H stands for the home team at home and A stands for the home team everywhere else (away).

An HFAr of one means there is no home field advantage; the team hits the same number of home runs relative to the opponent at home and on the road. A number greater than one means that the team has an easier time hitting home runs at home, thus a home field advantage. Anything below one means they are doing poorly at home, and not because of a park factor, as the other team would be subject to that as well. The ratio doesn’t have to be for HRs; it works equally for any stats, which may be especially useful to see how teams gain the upper-hand at home. Also, it varies as you would expect: with each HR hit at home the HFAr for HRs increases. If the other team hits a HR in the home stadium, HFAr decreases. Similarly, if the team hits a HR on the road HFAr decreases because we cannot attribute home-field HRs to being at home if the team hits lots of them everywhere. Finally, if the opponent hits a HR when the team is on the road, it increases HFAr by decreasing the team’s overall HR ratio, making the HRs hit at home relatively more noteworthy.

As I mentioned earlier, the Washington Nationals are a particularly interesting case. They stand atop the NL East at 52-38 coming into action on July 16th, largely due to their 30-13 home record (that’s a 22-25 road record if you don’t want to do the arithmetic). Their record is particularly interesting because they have a losing run differential- 362 RS, 369 RA- despite being 14 games over .500, leaving analysts to frequently postulate that they have a unique home field advantage in the spacious luxury of RFK stadium. Using HFAr, we can look at exactly where that advantage originates in terms of performance. Here are some of the most important HFAr numbers for the Nationals. (Note: Because I’m working with ratios, it doesn’t matter that the Nats have played more away games than home. The numbers standardize themselves when divided).

HFAr:

2B: 1.225
3B: 3.75
HR: 1.669
BA: 1.133
OBP: 1.149
SLG: 1.304
SB: 1.44
K: .723

Don’t look at the positive 2B HFAr and say “Oh, they’re better at hitting doubles at home.” That’s not actually true, they hit more doubles on the road, but their opponents hit a lot more doubles when the Nats are on the road. What you should really say is, “Oh, they’re better at hitting doubles at home relative to their opponents.”

A couple other interesting bits came up in these calculations that might help explain the Nationals’ home success. For one, they definitely show some of the home road splits you would expect for a team in a pitcher’s park, going from .251/.330/.386 at home to .264/.325/.403 on the road for a little improvement. In fact, despite the great home record, they are actually last in the major leagues in runs scored at home. The real splits are in their opponents’ stats: a putrid .240/.312/.329 at RFK, and a less Guzmanian .286/.353/.448 everywhere else. In other words, the Nats’ home field advantage comes from everyone’s bat turning into spaghetti upon entering RFK. Since HFAr doesn’t prefer a run scored to a run prevented, one could just as easily attribute the success to Washington’s pitchers stepping up at home. Either way, their opponents have been hurt far more by the park than they have.

Also, the 2B, 3B, HR and SLG numbers are much bigger than the AVG and OBP ones, meaning that other teams are able to scratch out singles nearly as well, but not get extra bases. This data bears out some of the conventional wisdom about home field advantage. For example, at home, a player knows when to stretch a double into a triple when hitting the ball into the RF gap, whereas he might just stop at second if he was uncertain of the OF contours. Also, power hitters may learn to hit more HRs in their home park (Jose Guillen aside) by tailoring their swings to the stadium’s dimensions. But beware of the sampling here, as the huge HFAr for triples is the result of only 4 three-baggers by visitors all year. The numbers may also level out more as teams take their second, third and fourth trips through DC and start to become accustomed to the confines.

As a final note, the HFAr figure for Ks of .723 still means they get an advantage at home, because teams try to avoid strikeouts. In the simplest terms possible, 12 Ks are better than 24 Ks for a hitter just like 24 HRs are better than 12 HRs. You could just as easily flip the numbers around and view it from a pitcher's point of view (desiring Ks) and get an HFAr of 1.38. Either playing in RFK helps their pitchers strike out their opponents more often, or helps their hitters strike out less often. Judging by the raw stats, it appears to be the latter.

None of this information provides conclusive proof as to why teams, particularly the Nationals, play so much better at home, but it gives a starting point for the discussion. At very least, we now know now much better they have been at home over the course of this half-season, and some of the differences allow us to make more educated guesses as to why that may be.