Tuesday, January 22, 2008

What about catchers?

This is the sixteenth (and final for now) part of my series on fielding in 2007. The table of contents for the entire series is listed below:

Basic fielding stats
Converting Zone Rating to something useful
Revised Zone Rating
Probabilistic Model of Range
Fielding Bible
Ultimate Zone Rating
Fan Fielding Survey versus range measures
Outfield arms
Ranking the second basemen
Ranking the shortstops
Ranking the third basemen
Ranking the first baseman
Ranking the center fielders
Ranking the right fielders
Ranking the left fielders
What about catchers?

The range statistics which have been the main focus of the series do not really work for catchers because range is not a large part of a catchers job. The catching position is the most difficult to quantify because the pitcher and catcher work together as a team more than any other players on the field. Endeavors such as game calling and handling of pitchers are believed to be important skills but they are very difficult to measure. It's really hard to know how much of good or bad pitching is due to the pitcher and how much is due to the catcher. Attempts have been made to do this but it's still an area that needs a lot of work.

Bill James first introduced Catcher ERA (CERA) in his Baseball Abstracts back in the 1980s. CERA is the ERA of a team's pitching staff when a particular catcher is behind the plate. The idea is that pitching staffs will have a lower ERA when a superior catcher is behind the plate. The problem with CERA is that sample sizes are very small for backup catchers (to which you are comparing the starters) so you need a lot of years of data. Over several years, CERA has not been found to be predictive. That is, individual catchers do not tend to have consistently low or high CERAs throughout their careers. It almost seems as if pitcher performance is independent of catchers! I don't think there are too many people (even sabermetricians) who believe that to be true but it is possible the the skill has been overstated by some. Anyway, it's an area which still challenges statisticians.

There are some skills which catchers have which are somewhat (not totally) independent of pitchers and can be measured. Those are throwing out base runners, preventing passed balls and wild pitches and avoiding throwing and fielding errors. These skills have been shown to be fairly consistent for individuals from year to year. Justin Inaz who writes the blog On Baseball and the Reds has developed an algorithm to combine these skills into a runs saved value.

He first calculates the major league average caught stealing (CS) rate. He then determines how many CS a catcher would be expected to make based on stolen base attempts against him and the average CS rate for all catchers. He subtracts the expected CS from the catcher's actual CS to get CS above above or below average. Finally, Justin converts that figure into estimated runs saved on CS. He goes through the same procedure with Passed balls and wild pitches and throwing and fielding errors. He then adds the numbers together to get a total runs saved value for the catcher.

For example, Pudge Rodriguez saved 2.9 throwing out base runners and 0.8 runs avoiding throwing errors. However, he gave up 4.3 runs on passed balls/wild pitches and 0.4 runs on fielding errors. Those numbers add up to one run allowed. That placed him 18th among 29 catchers with 700 or more innings. The major league leaders were the Cardinals Yadier Molina (11.5), the Mariners Kenji Johjima (10.3) and the Twins Joe Mauer (10.3). Justin lists all catchers with 400 or more innings in his article.

Does this method make sense? One way to answer this is to compare to the runs saved calculated from the Fan Fielding Survey (Fan Fielding Survey versus range measures). Tigers fans did not agree with Justin's algorithm as they ranked him 4th best in baseball. Overall, though, there turned out to be a moderately high correlation (.60) between the fielding survey and Justin's algorithm. That is a good sign that his number does measure something useful. He admits that it doesn't measure everything a catcher does but it appears to be a good start.

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