Tuesday, July 24, 2018
Why doesn’t xwOBA match wOBA?
?Logistics.
First, I'll tell you the right way, or at least a good way, to make sure that xwOBA and wOBA match. I would do a rolling one year period to make sure that they are equal. This way, by the end of the year, it would be a perfect match for that season. Why not use season-to-date? Well, what would you do after one week or one month, especially if that is a very cold month? Suddenly, forcing it to match at the April-2018-only level you'd actually be incorporating temperature, which is not what you are after. Or at least, it's not what I am after. Rolling it with a one year window and all that goes away. However, what it does do is that whatever property the 2017 season gets carried over to the 2018 season. Then again, as of Apr 30, 2018, we don't have great confidence as to what the rest of 2018 has.
Anyway, that's one way, and there are other ways to make sure xwOBA = wOBA at every point. Plenty of you Straight Arrow readers I'm sure have your own solution.
Now, logistics. There are two main logistical scenarios we have. The first is that we prepare media and other things that uses xwOBA. If it changes every day, that means that every piece of data has to get re-updated every day. The second one is to synch all our endpoints including Savant. It's a long process for all the endpoints to synch up. Sometimes we are even delayed, and when Savant is not updated by 11:00 ET, we hear about it. When we run Statcast Searches, we have to make sure all that is queryable at a play by play basis, so everything has to match everywhere else. So, we have constraints to deal with.
The plan was at the all-star break, we'd revisit the issue, and see if we could synch it up. Entering the 2017 season, we used 2016 as the model. And we really undershot. Entering 2018, we used the 2017 season as the model. And now we really overshot. That 2017 season, plus the season-to-date temperature has upset our plans somewhat. We are trying to figure out WHY before we make a wholesale change and create a 2018 model.
That said, by the end of the 2018 season, we will refresh. Now it's just a matter of the logistics until then.
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