Jordan Zimmermann’s Poor Stretch

From Jeff Sullivan’s chat that’s happening *right now* on the site:

9:02 Comment From bdhudson
Jordan Zimmermann is developing a really unpleasant trend.

9:02 Jeff Sullivan:
This is an example of a prompt that sends me to 60 seconds of research

9:02 Jeff Sullivan:
This is why my chats go so much slower than others do

9:03 Jeff Sullivan:
Zimmerman’s first 13 starts: 2.00 ERA, 4% BB, 17% K

9:03 Jeff Sullivan:
Zimmermann’s last 12 starts: 5.27 ERA, 7% BB, 20% K

This is a bit difficult in terms of DIPS, maybe — Zimmermann has been striking more people out, but still undergoing the regression that we thought might be coming when we last ranked him among the starting pitchers. Regression that we predicted because he doesn’t strike a ton of people out.

The easy way out of any paradox here is the concept of K%-BB%. The basis for kwERA, this simple formula beat out the other predictors in an in-season test last year, and it’s basically the backbone of DIPS (Defense Independent Pitching Statistics) theory. Get the outs you can get all by your lonesome, and limit the guys you put on base on your lonesome, and all the rest of it will even out eventually. You can see that Zimmermann’s K%-BB% is the same in both stretches. His batting average on balls in play through June was under .250, his BABIP the last two months over .320. Presto bingo bango blog post.

Baseball is a little more complicated than that. Why is Zimmermann suddenly a high-strikeout starter?

Looking at his pitching mix, he’s thrown 14% curves since July first, and that’s up from 12% career. That’s just 17 more curves, though, over nine starts. That’s not even two extra curveballs per start. Probably not the cause of a change in statistical profile. The curve might have lost some horizontal movement (as much as an inch and a half) as well as some vertical movement (an inch), but it’s also getting fewer whiffs. In fact, it’s not the greatest pitch, as it gets below-average whiffs and grounders, and according to Brooks Baseball, is a ball more than any other pitch he throws. Probably not the curve.

It’s always worth checking the pitching mix when you see a pitcher’s numbers take a detour. More curves could have meant more strikeouts and more walks for Zimmermann, and in fact they still could, despite the deficiencies of that particular pitch. But the change in mix was so small, it doesn’t seem like a good idea to point in that direction this time.

No, this time, the Standard Blog Post might have had it right. When June ended, Zimmermann’s BABIP was .238. Since then, it’s been .342. And yet Jordan Zimmermann is mostly the same guy he used to be. This is the beauty of DIPS.



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With a phone full of pictures of pitchers' fingers, strange beers, and his two toddler sons, Eno Sarris can be found at the ballpark or a brewery most days. Read him here or at October. Follow him on Twitter @enosarris.


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Dan Rozenson
Guest

I watch Zim closely. Part of it may be simple regression, but part of it is also that he’s made more mistakes lately. More balls left over the plate he had meant to put on a corner.

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