HFAr through the Majors

The author’s job is to get the reader interested. If I’m writing a book, the first chapter needs to be worthwhile or you’ll put it down. When I introduced the Home Field Advantage ratio, it needed a snappy kickoff, or everyone but the most analytically-minded would forget about it by the end of the article. I decided to apply it to analyzing the Nationals’ success right off the bat, and, in so doing, I left a lot of ground uncovered. Today I will go back and retrace some of my steps to explain how HFAr functions as a league-wide tool.

Even though the Nats example gave a pretty demonstrative case and helped me make some of the intricacies of HFAr clear, it may have been in some ways misleading. Perhaps the most important aspect left unclear is that most teams have an HFAr greater than one for important categories. In other words, home field advantage is real. If you don’t believe me, look at the standings, where 22 of the 30 MLB teams have a .500 or better record at home. League average varies from stat to stat, but HFAr will usually average somewhere over 1.1. Also, it must be clear that there is no single HFAr stat to explain how well a team performs at home relative to road performance; it can only explain specific statistics. The strength that counterbalances this particular weakness is that any HFAr measure simultaneously takes into account production and prevention. Much like the Pythagenport standings encompass runs scored and runs allowed, each HFAr is a ratio of how much of a certain stat a team produced to how much it allowed.

Since the correlation between run differential and winning percentage is already well established, I decided to go another route and examine how OPS impacts winning at home and on the road. If OPS was a perfect measure of offensive production, OPS-HFAr would fully explain the difference between a team’s performance at home and on the road. Since OPS is flawed, OPS-HFAr cannot fully explain run prevention or run production differentials, missing by the margin set by the OPS limitations. Today I’ll go over some of the OPS-HFAr data for the major leagues, and tomorrow I will show some graphs that demonstrate how much more effective HFAr is at explaining home-road winning splits than OPS.

OPS-HFAr rankings:

Houston: 1.43
Colorado: 1.27
Atlanta: 1.24
Washington: 1.23
New York (A): 1.20
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17. Minnesota: 1.12
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25t. Philadelphia: 1.04
25t. Kansas City: 1.04
27. Anaheim: 1.02
28t. Arizona: 1.00
28t. Seattle: 1.00
30. Chicago (A): .99
Mean: 1.127
Median: 1.13, 1.14
Mode: 1.14

At first, it seemed to me that hitter’s parks would populate the top of the standings, because so many teams hit extremely well at home and struggle on the road in Colorado fashion. As my Nats study indicated, however, teams have a very difficult time adjusting to an extreme pitcher’s park, hence the high marks for Washington and Atlanta. And sure enough, the top three teams in Winning Percentage at home are all in the top four in OPS-HFAr, Washington, Houston and Atlanta.

The reason OPS-HFAr is better at explaining a winning record than OPS alone is that it takes pitching and defense into account. The White Sox have only a .739 team OPS to go with their mind-blowing .678 Winning Percentage, but they prevent other teams from having a high OPS by playing two CFs and pitching above their collective established level of performance. I will have more to say about correlation tomorrow as the graphs do a better job explaining regression than I can do in words.

A couple of other interesting notes:

-All of the most extreme home or road W% are teams with obscene losing records on the road. No team has posted a .700 record at home or on the road, but Colorado (.163), Cincinnati (.262), Tampa Bay (.234) and Kansas City (.289) have all fallen below the correlative .300 W% on the road, with Houston (.304, but climbing) within smelling distance.

-Speaking of Houston, it is strange to see a team with such a tremendous home-road split and an overall record near .500. Intuitively, a team is either good or bad, and a good team would win at home and on the road, while a bad team would lose at home or on the road. Home field advantage can explain a bad team playing well at home, like the Rockies, by giving them a repeatable leg up. But a team that isn’t great and isn’t terrible finding a way to be great at home, but remain terrible on the road (.682 to .304) is surprising.

-Only CHA and SEA post a home field disadvantage in terms of OPS (SEA rounded up to a 1.00 HFAr), and both are slight. Five teams, though, have found a way to have a higher road winning percentage than home, including Chicago. The other four have performed well at home, but not won games. San Francisco is the most egregious offender, approaching league average with a 1.10 OPS-HFAr, but still having a .435 home W% to .444 on the road.

-This research demonstrates just how similar Cleveland and Detroit have been this year. The teams’ OPS-HFAr is identical out to four decimals, and they are within ½ a game at home and 1.5 games on the road.

-The Twins don’t show any strong tendency toward home or road dominance. Their OPS-HFAr of 1.12 is just a tick below league average, meaning their home field advantage is still there, but the baggy isn’t the game-breaker everyone has always made it out to be. I will be interested to see in looking at old data if their advantage changed when their speedy team switched from Astroturf to Fieldturf. Finally, in the Twins’ case, most of the advantage comes from improved hitting at home. Their opponents’ OPS drops from .745 to .721 in the Metrodome, while the offense sees a much greater gain, going from .695 to .752.

-Although it would have been prudent to check it out right away, my hypothesis about the Nationals holds true for these rankings, as they gain nearly as much from playing at RFK (about 11%) as the worst teams lose. That statement makes Houston’s achievement(?) that much more astonishing.

And in case you’d forgotten, I’ll have much more on the subject up on Tuesday afternoon.