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Wednesday, October 19, 2011
Playoff home advantage, NL/AL
Poz reels off some interesting info.
It probably helps to understand the home/away context. A team will score about 0.4 more runs per 27 outs at home than on the road. (This is why for example, they have a .540 win% at home: 0.4 runs = 0.04 wins, and 0.04 plus .500 is .540. Isn’t math fun?)
Another interesting thing to note is that a pitcher’s wOBA is around .160, while a DH is around .350 (more or less, and depending on the year). Pitchers come to bat 2.5 times, and then you have PH the rest of the way (PH are around .300 wOBA, and we’ll give them 1.5 PA). Remembering that to convert wOBA to runs you divide by 1.2, and we get: DH over P = (.350-.160)*2.5/1.2 = 0.39 runs. DH over PH = (.350-.300)*1.5/1.2 = .06 runs. So, the DH advantage is about 0.45 runs per game. Basically, the DH advantage is about as large as the home field advantage.
Ok, so he notes that:
On the road, with the pitcher hitting for himself, AL teams have averaged about 3.77 runs a game. With the DH, they average about a half run more per game. I think that fits in with what you would expect.
We have three effects: the home/away, DH/P effect, and the unfamiliarity of playing “out of position” on the road (AL team using a P, NL team using a DH).
So, being at home, AL would be +.4 more runs than on the road. Being at home, DH generates +.45 more runs than P/PH. Being at home, the familiarity of playing by your rules, you’d get some positive effect, say something like +.15 runs (just pulled it out of my a$$). The total of these two is +1.00 runs, but Poz is reporting only +.50 runs scoring at home for AL teams than on the road. There’s another 0.50 runs unaccounted for.
Anyway, we go on to the NL:
The National League, though, offers the shocker. At home, with pitchers hitting, they average 4.15 runs per game, which is pretty close to what American League teams score at home. But on the road, using the DH, National League teams have scored only 3.4 runs per game, meaning they score seven-tenths of a run LESS per game with the DH than they do with pitcher’s hitting.
So, at home, we’d expect them to score +.4 more runs. The DH impact would mean scoring -.45 runs at home (i.e., fewer runs at home than on the road). And then, some impact for familiarity at playing by home rules of +.15 runs. In total, we’d expect NL teams to score +.10 more runs at home than on the road. Poz is reporting that they score +.75 more runs at home than on the road. That’s an extra 0.65 more runs unaccounted for.
Is it possible therefore that there’s a huge familiarity factor of playing by your home league rules, way above the +.15 I was originally contemplating?
I mean just look at the data right here:
American League home record: 44-21 (.677 winning percentage)
National League home record: 37-29 (.561 winning percentage)
So, the average playoff team at home wins at close to a .620 clip, far higher than the .540 that you’d see in the regular season. And getting a +.08 win advantage, that’s a +.80 run advantage.
And that pretty much closes the gap in my numbers above.
That’s +.08 win advantage at home (over and above what you’d see in the regular season) is almost two standard deviations from the mean. It’s possible that this is just small sample size. But, seeing that we have a huge parameter here (playing by home-league rules), a .540 prior would seem to be too low to test against.
I’d love to see more data breakdowns and analysis on the AL/NL breakdown, including home-field advantage for intra-league playoff games as another comparison point.
Thanks Joe, learned something new today!
Very interesting! I bet small sample size is most of it, but I stand to be corrected by new evidence.