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Big Changes coming to Fangraphs D-backs pages?

Turns out Changes were not that big

San Francisco Giants v Arizona Diamondbacks Photo by Christian Petersen/Getty Images


I was reading the article on the D-backs collapse over at FG, and that lead me to read Jeff Sullivan’s article on the Humidor from August 16th, which I missed previously.

In that article Jeff makes a pretty strong case for Chase Field becoming much closer to a neutral run environment this year. In fact, I had previously been informed that FG was using a neutral park factor for 2018. However that does not appear to be the case. From the last paragraph of the article:

For outside observer purposes, I don’t know how much this really matters. In the short-term, because our FanGraphs park factors take a while to update, know that Diamondbacks hitters are being underrated by wRC+, and Diamondbacks pitchers are being overrated by ERA-. That’s not too terribly important.

Actually for most of the year wRC+ was ranking higher than OPS+, which uses multi year park factors and for sure is still treating Chase as a hitters park due to that. But recently I happened to notice in passing that the OPS+ and wRC+ numbers had started to converge, but didn’t pay it too much attention.

On twitter I reached out to Jeff, and he referred me to David Appelman Below is the exchange:

The response and my follow up question:

So this is actually big news. Jeff may say it’s not terribly important in the article, but I disagree. The wRC+ and WAR for hitters is going to go up, possibly by a good deal, and the ERA- and Pitcher WAR should go down, again, perhaps by a good deal. This could have a fairly big impact on how DBacks players are evaluated, not just by us here, but even those awarding contracts, preparing arbitration arguments, etc. It also could impact post season awards voting as well.

I’ve downloaded the FG Advanced and Value pages for Hitters and Pitchers, and will check them tomorrow and the coming days to see if they changed, which they certainly should if the park factor is changed from 112 to 102 ! I would expect to see Goldy’s wRC+ and WAR to jump, and Corbin’s WAR to go down....etc. We’ll see if that’s the case.

Stay tuned.


David Appelman of Fangraphs was kind enough to spend time to answer all of my questions and clarify the process by which they create the metrics and stats on their terrific site. I’d like to thank him again for his time, patience and transparency. We are lucky to have such a wonderful resource run by open and honest people.

The impacts and effects of the updates are far less than originally anticipated. Below is the exchange we had which explains most of it:

DA: There are two different park factors used for batting / pitching WAR. Runs for batting, FIP for pitching. The Runs park factor decreased, but the FIP park factor remained pretty similar.

JS: So I notice there is a bit more movement in the RA-9 WAR . I assume the Runs factor is used RA-9 WAR ?

DA: Right, RA-9 uses the Runs PF

JS: OK.....ERA- as well ?

DA: Yep, that also uses the Runs PF

Also, depending on how many years are in the PF, it is regressed different amounts.

So, now that there is only 1 year, it’s regressed pretty heavily.

Thanks for bringing this up. We had meant to make it a new park, which typically happens automatically with new park ids, but this ended up being kind of a weird situation. Significant fence moving will change the park id, but this just didn’t and ended up being an oversight on our end when we started updating PF in August.

I believe prior to the parks being updated in August, we did have it set at 100.


So this really helps us to understand a lot. I appreciate David clarifying that there was an update done in August, and that the PF was originally set to 100 as I was originally informed. When they did the August update then, they did not “make it a new park” and were using multi year factor which of course made it a hitters park. Now that they have made it a “new park”, the values are closer to a neutral park. However it’s also really important to note his point about the factors being heavily regressed due to only having one season of data. So that mutes the changes.

The other important point he mentions that there are two different factors, one for runs and the other for FIP, and they are not the same. Again this makes sense, as FIP does not include balls in play.

In the pitcher value section at Fangraphs they show an RA-9 (Runs against per 9) and also their primary WAR metric, which is FIP (Fielding Independent Pitching) Based So on the pitching side the impacts are a little more on the RA-9, but almost no change to the FIP WAR.

Finally, I’m sure everyone wants to see just what the changes were. When I compared the before and after, I noticed that the Fielding and Base running numbers had changed as well, in a few cases by quite a bit. Some positive, some negative, but mostly negative. David explained that the last UZR update was done on the 14th, so it had been 11 days since UZR Fielding numbers had been updated. I didn’t know that that fielding was not updated every day, and David indicated someday they might be able to get the part of the update done on a daily basis. Below I’m just showing batting, baserunning, and fielding runs and final WAR. However you can see the full table including positional adjustments, replacement runs, league adjustments, etc etc HERE . As always, if you are not familiar with how WAR is constructed, you can ready about it from their THIS ARTICLE


So as you can see the Batting Runs increased by 35 overnight, but WAR only increased by 2.5 due to decreases in fielding and baserunning runs over the last couple of weeks. (Yes, this confirms what we saw with our eyes).

Here are the individual hitters. I took out Pitchers and a few guys with little playing time. Since it was an overnight update the guys that had really good games last night get slightly more bump. The fielding updates leave me with one more question which is why there would be change to a few guys that haven’t played in the last 11 days, like Dyson +0.2 fldg Runs...but it’s not a big difference and not important. One other point, I lost the file that had Sept 26th wRC+ numbers, so I don’t have them to compare, but the batting runs change gives you a good idea of the impact.

Here is the team level for pitchers:

Here are the individual pitchers, with a few guys that are no longer on the team or have pitched very little removed. It’s sorted by RA-9 WAR as the WAR was change was neglible .

Since I didn’t post the hitters wRC+, I’m not going to both with Pitchers ERA-. But for example Corbin goes from ERA- 75 to 79 despite not having pitched, but his FIP- stayed the same at 60. Robbie Ray went from 91 ERA- to 95 ERA-.

So all in all, much adieu about nothing in terms of changes to the tables and rankings. For someone like me, 2-3 WAR on team level is somewhat significant, but in the big scheme of things, it’s really not. But I’m glad we were able to gain a better understanding of how FG works, and it’s good that they are using the correct PF now.