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Friday, March 11, 2011
Poz on offense stats
His takedown of batting average is a re-run, but worth re-reading. Imagine being in court, having the prosecutor read Poz’s post on batting average, and you on the defense have no choice but to say: “we accept that statement as factual”. And then after accepting the facts, you argue that it makes sense that batting average is one of the prime stats to use.
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One of the coolest stats out there is WPA, which stands for Win Probability Added, which is a name that I don’t think helps the cause much. There are certain words that scare the bejeebers out of people. Linear Weights were like that for me. I would see anything mashing those words together—“linear” and “weights”—and I would kind of freak out.
I’d be happy to hear of alternatives. WPA is the change in win expectancy assigned to the players involved in the play. I agree that the description may sound off-putting. Suggestions?
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I cracked up here:
The stat wOBA looks scary because any word where you make the first letter lower case and the rest upper case is scary. It doesn’t matter how harmless or happy the word really is. Look:
eLMO
bABY
fARVE
The one thing I want to say about wOBA is about the number “1”. The numerator of wOBA is positive events. An average positive event is “1”, just like in OBP. Actually in OBP, EVERY positive event is a “1”, be it a walk or a HR.
In wOBA, we see that a single is just a bit worse than an average positive event. That’s why you give it 0.9. A walk is alot worse than an average positive event, so it gets 0.7. A HR is far better than an average positive event, so it gets 2.0. Basically, the whole thing is centered around “1”. An average positive event is 1, and then you simply use that as the centering point.
I know way back when wOBA was first introduced in The Book, there was alot of push back that I should have used batting average as the scale. Except I couldn’t do that. If I did that, then the average positive event would have to be 0.8. A single would be 0.7, a HR would be 1.6. See? There’s just nothing really to center everything. Indeed, a double would be worth 1.0. Not to mention that OBP, not batting average, is what baseball is all about. OBP already has plate appearances (PA) as the denominator. If I scaled wOBA to batting average scale, how can I explain that the denominator of this metric would be PA? Anyway, that’s why wOBA makes sense to me.
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