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Examining the Wizard: Roy Oswalt's DIPS ERA

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I need to preface this with: I'm not 100% that the DIPS ERA I'm about to report is perfect.  I am still waiting on a data set from 2008 that I purchased to help me correct some possible differences in batted ball results from the 2006 data set I was able to find online.  However, I don't expect that margin of error to be more than 3 runs, which over 150 IP (where Roy Oswalt is now) is only a difference of is a +/- .198 ERA points.  So you can keep that in mind as you look at this.

Using the method that I outlined in Baseball Knowledge 201: DIPS > ERA, and data obtained from (it's linked below), I broke down Roy's batted ball data to correct for a lower line-drive rate and his slightly inflated HR/FB rate.  I'm uploading a spread sheet that you can play around with that has all the information and calculations I performed.  All the nitty gritty of the math is on the there.  Anyone with a firmer grasp of the Base Runs formula, please feel free to chime in on where I screwed up -- if I did (crosses fingers).

The result was surprising to me, at first.  Using the DIPS 3.0 methodology, I determined that Roy Oswalt owns a DIPS ERA of 4.85.  My jaw dropped and I went back over all the math and the spread sheet formulas about 10 different times when I saw that.  I recalculated the batted ball averages and read every article I could find on Base Runs.  I was left with the same number.  Then it occurred to me that I should stop disbelieving and start hypothesizing.

These are the things we know about the Astros and Roy Oswalt (Source and Source):


  • They have the second best team RZR (click if you're unfamiliar with RZR)
  • They have the best infield RZR.
  • They are slightly below average in outfield RZR, but Bourn and Pence are the cream of the crop in the respective positions for RZR.  So we basically have a 2/3 of an stellar outfield; with Bourn probably taking at least 1/12 of Carlos Lee's territory.
  • Roy Oswalt's In-field fly percentage is down (6% compared to a career rate of 11%).
  • Roy Oswalt's LOB% is also well below his career levels (72.8% to 76.5%)
So what do all of those things mean?  Mostly it means that because the Astros defense is so far above league average, that a DIPS ERA will naturally be inflated, because correcting his line downward.  Further, it means is that even though Roy has a great defense behind him, he's not taking advantage of it by pitching well with men on base.  As result, he's raised the rate at which he is facing batters.  The more batters he's facing, the more likely his is to allow ball to be put in play and the more balls are put into play the worse things get.  Interesting to note, that if his results were in fact league average, we'd expect on 17.5ish HR against him. That last two points are should be alarming for Astros fans.

The reason I am truly excited to get my hands on the 2008 batted balls data set, is so that I can break up Roy's batted ball data to pre and post ASB splits.  With this, I am hoping to see that Roy really was just a bad pitcher when he had a irked hip.  Once he rested and rehabed, Roy has really returned to form.  My hope, actually all of our hope's should be, is that Roy's split DIPS ERA will show that luck wasn't to blame for his awful start, but bad pitching.  While people far more skilled at database coding than me will have to determine if he was ineffectively pitching from the stretch using pitch/fx, I think that might be the conclusion we can reach; if the numbers confirm my hypothesis.  This would be good news for Astros fans.

Like I said, I'm not fully sure of that all of the numbers are perfect, but the margin of error should be relatively minor.  To repeat, I urge those who want to check my math to do so and also throw out their own hypothesis about why it is that Roy's DIPS ERA is .75 runs higher than his actual ERA?

Here is the  roydips3.0 (excel)  spread sheet in Excel.  If you want it in CSV post your request in your comment and I'll shoot it to you in an email.