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February 28, 2014

Pebble Hunting

The Pitchers Who Changed PECOTA's Mind

by Sam Miller


It’s a feeling we’ve brought up a lot this winter: Pitchers seem like they are capable of changing our minds much more quickly than hitters can. A bump in velocity (like Ubaldo Jimenez) or a move to the bullpen (Will Smith) or a return after years away (Scott Kazmir) can radically reshape how we assess a pitcher's future.

Which suggests we should be open to radically different projections for a pitcher from year to year, and yet! There’s a case to be made that this unpredictability should actually make a projection system even more conservative when evaluating pitchers. As quickly as a pitcher can change our minds about him, he can unchange our minds, lose the velocity or move back to the rotation or undergo a surgery that fixes him. So, when in doubt, regress.

It usually takes quite a bit of time for PECOTA to really change its mind about pitchers. Of the 819 pitchers for whom PECOTA issued projections in both 2013 and 2014, 766 are projected to this year produce a WARP within 1.0 WARP of what they were were projected to produce last year. Of the 53 whose projections changed by more than one win, 45 saw their projections drop. So what must a pitcher do to make PECOTA fall suddenly in love? Answers imminent!

Repeating the exercise we did with hitters earlier this week, here are the pitchers whose 2014 projections are most improved from their 2013 projections:

LASTNAME FIRSTNAME 2014 projection 2013 projection Change
Fernandez Jose 4.6 0.5 4.1
Wacha Michael 3.2 0.5 2.7
Wood Alex 1.7 -0.3 2
Gausman Kevin 1.4 -0.2 1.6
Ryu Hyun-jin 2.3 0.8 1.5
Gray Sonny 1.4 0 1.4
Corbin Patrick 1.6 0.5 1.1
Cole Gerrit 1.9 0.8 1.1
Perkins Glen 0.7 -0.3 1
Salazar Danny 0.7 -0.3 1
Hunter Tommy 0.8 -0.2 1
Wisler Matt 0.9 -0.1 1
Collmenter Josh 1.4 0.4 1
Quintana Jose 1.6 0.7 0.9
Uehara Koji 1.8 0.9 0.9

So think about Billy Ray Valentine in Trading Places. If you had to project how well he would do as a managing director at a billion-dollar commodities brokerage, you would start with the limited information you have: his performance as a street-level hustler. How is he, as a street-level hustler? A grade-65 street hustler? Well, billion-dollar business environments are more difficult than street hustles. More-educated competition, more advanced training required, etc. So you’d discount his grade as you increase the level of difficulty. And, because the skills needed for street hustling might not translate perfectly to the board room, you’d probably hedge a bit and make your projection a little more conservative. Further, you don’t know that much about his street-level-hustle work; you just started watching him this very afternoon! So regress a little more.

And here is what we knew about Jose Fernandez before 2013:

  • 79 innings of low-A, 1.59 ERA
  • 55 innings of High-A, 1.96 ERA

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Related Content:  PECOTA

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