Catcher's ERA, a New Defensive Measure?

THE FOLLOWING IS REPRODUCED WITH THE APPROVAL OF ITS AUTHOR. WE WOULD LIKE TO THANK MR. ROSCIAM FOR ALLOWING US TO DO SO.


Catcher's Earned Run Average (CERA)
Meaningless Stat Or An Effective Measure?
by Chuck Rosciam, SABR Member

A discussion of the value and shortfalls of the statistic called Catcher's Earned Run Average (CERA).

INTRODUCTION

Most experts (meaning managers, coaches, pitchers and catchers) believe that the aspect of the catcher's job that has the most impact is his game-calling, that is, his ability to work with pitchers and help them throw more effectively. The standard and most acceptable measure for a pitcher is the Earned Run Average (ERA). Baseball is a game that has statistics for virtually everything, but there seems to be precious little time and energy devoted to measuring how well catchers perform at calling the game. Rather, we see catchers’ defense measured by how many base stealers they throw out or how many passed balls or errors are charged against the backstop. A recent attempt at measuring a catcher's defensive skills is the CERA, which basically is the Earned Run Average of the battery (catcher and the pitchers on a team) for each specific catcher as compared to all other catchers and their batterymates.

The most comprehensive published study on the subject is Craig Wright's "Catcher's ERA" in his book The Diamond Appraised. Craig defined a process whereby catchers on the same team can be compared by how well a common set of pitchers perform with each catcher. That is, Catcher A's and Catcher B's CERA for Pitcher 1 are compared for the differences. The resultant CERA can be used to draw a conclusion as to the intrateam value among catchers.

PROBLEMS WITH CERA

However, there is a problem with this straight forward approach, as noted by Keith Woolner in his study published in Baseball Prospectus. The problem is sample size. When attempting to use "matched pitchers" for a team's catchers, there are wide fluctuations in the number of innings especially for the backup catchers. These variations between catchers' innings and hence their CERA may be "natural variation" attributed to simple chance or they might be the result of true game-calling ability.

Furthermore, there is the situation of the alternate (backup) catcher being used as a late inning substitute and paired with mop-up bullpen hurlers, generally in a losing cause. The starting catcher would have very few innings with these bullpen guys (usually with a high ERA) while the backup catcher would have few innings with the #1 and #2 starting pitchers (who usually have lower ERA's). Then there is the phenomena of Grag Maddux. When he pitched for Atlanta he preferred to throw to backup catcher Eddie Perez instead of the number one guy, Javy Lopez. Because of Maddux's preference and low ERA, this would preclude any matched pairings or if pairings were ignored the scales would tip in Perez's favor.

The next concern with CERA (and by no means the last) is the way that CERA is now being captured and presented in various publications which form the core of the CERA statistical library. The Bill James Handbook formerly published by STATS, Inc. and now ACTA, do not use matched pairings, but rather capture all of a catcher's innings and earned runs regardless of the pitchers involved. It is a raw total report that in and of itself is very misleading.

In Table 1. below you have two equal catchers (A and B) who have the very same CERA for each and every pitcher (1, 2, and 3) they caught. The only difference between the catchers is in the number of innings caught for each pitcher although their cumulative total innings are identical. "CATCHER A" only caught 50 innings with "PITCHER 2" (ERA of 4.50) while "CATCHER B" caught 110 innings and had the identical CERA. "CATCHER B" is penalized (in his cumulative CERA of 3.86) for doing the same job as "CATCHER A" only because of the way the CERA raw total statistic is formulated.

***TO SEE THE TABLES AND READ THE REST OF THE ARTCLE LINK TO THE FOLLOWING ADDRESS:
http://www.baseballcatchers.com/cera1.htm