Exploring Chase and Watch Rates

File under "sausage". Lab notes + some rankings + one graph.  And downloadable data (good idea, JK).

One aspect of pitching analysis I enjoy is looking at three simple metrics - really two.  One is the ball to called strike ratio (B:CS).  It's useful in a few ways - but, at a glance, a poor ratio on a fastball (for example, 2.5:1) it makes me wonder if he's wild (i.e. missing high) or tentative (missing wide).   Again, this is just one element or aspect of a pitcher (or, more commonly, a hitter).

When I add in two versions of swing rate, I get a picture of control and deception.  If a breaking pitch is chased out of the zone AND watched in the zone, I figure the pitcher must have control and some form of deception - whether it be keeping the hitter off balance or nasty stuff.  I usually don't consider these too much when looking at pitchers as a whole, however.  Just within pitch types, maybe counts etc.

But, I decided to give it a whirl, fired up all pitchers in 2008 with more than 500 pitches PA in the PITCHf/x database.   

As a broad statement, batters swing at a third of all pitches out of the rule book zone, and also take a third of those within the zone.  These reference points are the same across the 2008 and 2007 samples, or roughly so. 

The sample averages:
B:CS   2.1
Chase .331
Watch .337

I use Watch, the inverse of a simple swing rate in the zone since (a) it lines up nicely with the Chase value and (b) the convenient proximity to what also would be a good batting average - easy to digest.

A couple things stand out - the pitchers that fall in the upper levels of all three metrics are good pitchers, the pitchers at the bottom aren't as bad as those at the top are good, however.  Lastly, it seems chase rate is more meaningful, although, in combination with other metrics, watch rates can still be helpful.  I won't exhaustively explain all this, but I think/hope a quick run through some numbers will make that clear enough.


The following 11 pitchers share three characteristics:

  1. B:CS ratio below 2.1
  2. Chase rate above .340
  3. Watch rate above .357

Those cut-offs are fairly arbitrary, and I'll throw in tRA+ from StatCorner for a reference.

first last # B:CS Chase Watch tRA+
Doug Brocail 1062 1.9 0.350 0.362 121
Jesse Carlson 800 1.5 0.350 0.389 116
Matt Herges 1008 1.8 0.357 0.388 92
Cliff Lee 3257 1.6 0.375 0.369 141
Scott Lewis 529 1.9 0.343 0.390 99
Sean Marshall 1056 1.8 0.345 0.377 118
Ricky Nolasco 3141 1.6 0.363 0.358 117
Joakim Soria 1030 1.6 0.351 0.375 137
Ryan Speier 737 1.7 0.341 0.382 109
Brad Thompson 953 2.0 0.351 0.368 93
Brandon Webb 3258 1.9 0.371 0.394 136

No real dogs, the worst are just below average.  A few top shelf starters and relievers are in there, too.

Now, on the flip side of the equation, the wild and un-deceptive.

  1. B:CS ratio above 2.1
  2. Chase rate below .297
  3. Watch rate below .310

13 pitchers made this cut. 

first last # B:CS Chase Watch tRA+
Jason Frasor 820 2.2 0.237 0.305 71
David Purcey 1096 2.6 0.260 0.299 97
J.A. Happ 585 2.3 0.263 0.304 105
Roy Corcoran 1100 2.5 0.276 0.309 122
Warner Madrigal 613 2.2 0.278 0.280 90
Ryan Feierabend 675 2.4 0.282 0.245 70
Oscar Villarreal 581 2.4 0.285 0.300 99
Greg Smith 3037 2.5 0.286 0.296 90
Adam Eaton 1744 2.5 0.287 0.293 110
Octavio Dotel 1179 2.2 0.290 0.292 120
Jack Taschner 887 2.7 0.292 0.294 108
Dennis Sarfate 1461 2.7 0.292 0.307 105
David Weathers 1154 2.2 0.296 0.302 82

Not as bad as I would've expected after the first group.  The median tRA+of the 2nd group is 99, while the first group is 118.  The best pitchers in the "wild" group are just ahead of the middle of the pack of the first group.

So, what does correspond with success, in a broad sense?  I think we all know the results of a bad B:CS ratio.  But what's more important - chasing or watching? 

Intuitively, I'd say chasing.  It leads to higher whiff rates and less hard hit balls.  The penalty for relying on too many chases is too many walks - so watch the B:CS ratio that's inflated when a pitcher has a low chase rate (that's just an idea, nothing I've proven out).   The penalty for relying on too many watches is getting crushed every so often - so watch the nkSLG and TBP (also just another idea).

Here's a run around the distribution - 9 "extremes", and, in the center square, Mr. Average.

Cwbcs01_medium

Notice the high chase guys picked out in their quadrants are Brandon Webb, Cliff Lee, Mariano Rivera and Jonathon Papelbon.

If you want to see the whole list of 425 pitchers and their numbers (no tRA+, feel free to add it), you can grab/view this Google doc.  I'll go back to Mom's BasementTM, where my lab is obviously located, and explore the notions around chase/slg and watch/b:cs.

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