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A Note on K/BB
Posted By Bill Baer On November 27, 2012 @ 8:05 am In MLB,Philadelphia Phillies,Sabermetrics | 13 Comments
Over at Beyond the Box Score, Glenn DuPaul (@Glenn_DuPaul) recently wrote a great article about the flaws inherent to the strikeout-to-walk ratio (K/BB) stat. It’s one you’ve seen in many pitching-related articles here, and one I’ve generally just used unthinkingly lately due to its comfort and ease of use.
My primary issue with the statistic is the fact that walks are in the denominator. Strikeouts are just as (if not more) important as walks, however when walks are the denominator, a pitcher who is very good at not walking batters, but not a great strikeout pitcher will end up with a high K/BB. It’s simple math.
I prefer to stick with plate appearances as the denominator. Strikeouts minus walks, then divided by plate appearances — (K-BB)/PA — makes for a much more valuable statistic, in my opinion.
For those who feel like that statistic is too much work when K/BB is already calculated right there for use, think of (K-BB)/PA in a different sense.
(K-BB)/PA is the same thing as K% minus BB% (both statistics that are readily available). It’s simply the percentage of batters that a pitcher strikes out minus the percentage of batters that same pitcher walks.
DuPaul then offers a few examples of how K/BB can be a bit misleading, even citing former Phillie Joe Blanton.
Unfortunately, DuPaul’s more technical stat isn’t widely available on FanGraphs and Baseball Reference (yet?) so it won’t be as convenient to cite, but going forward, I will make a concerted effort to use it instead of K/BB. Hopefully the change leads to more accurate analysis going forward.
What follows is a comparison for Phillies pitchers who faced at least 200 batters during the 2012 season.
Strikeout rate (K%), high to low
|Antonio Bastardo||36.2 %|
|Jonathan Papelbon||32.4 %|
|Cole Hamels||24.9 %|
|Cliff Lee||24.4 %|
|Joe Blanton||20.5 %|
|Roy Halladay||20.4 %|
|Vance Worley||18.1 %|
|Kyle Kendrick||17.2 %|
Walk rate (BB%), low to high
|Joe Blanton||3.2 %|
|Cliff Lee||3.3 %|
|Roy Halladay||5.6 %|
|Cole Hamels||6.0 %|
|Jonathan Papelbon||6.3 %|
|Kyle Kendrick||7.3 %|
|Vance Worley||8.0 %|
|Antonio Bastardo||11.6 %|
Strikeout-to-walk ratio (K/BB), high to low
(K-BB)/PA, high to low
|Jonathan Papelbon||26.1 %|
|Antonio Bastardo||24.6 %|
|Cliff Lee||21.1 %|
|Cole Hamels||18.9 %|
|Joe Blanton||17.3 %|
|Roy Halladay||14.9 %|
|Vance Worley||10.2 %|
|Kyle Kendrick||9.9 %|
There isn’t a sea change between K/BB and (K-BB)/PA. Perhaps the biggest beneficiary is Antonio Bastardo, who had the third-lowest K/BB of the eight pitchers listed, but moved up to second-best in (K-BB)/PA. Joe Blanton, as mentioned, isn’t quite as attractive in this new light. Compared to the 11.3% league average, though, most qualified Phillies pitchers performed well.
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