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On Catcher Defense

In Baseball on October 21, 2013 at 8:50 pm

Baseball statistics have become more sophisticated in the last decade. So why is it still so hard to measure defense?

The last decade has been a veritable golden age for statistical analysis in baseball. In the decade since Michael Lewis wrote Moneyball, front offices and fans have shed the shackles of the box score and embraced sabermetric-style statistical analysis. Metrics like VORP, PECOTA and WAR have revolutionized how we value position players, while statistics like FIP and ERA+ evaluate pitchers without the variables of defense and ballparks. Even the previously nebulous subject of defense has been refined with statistics like UZR and the Dewan Plus/Minus system, revealing that good defense can be just as valuable as offense. But while these and other statistics have changed the way we analyze baseball, one area continues to baffle sabermetricians — the defensive value of catchers.

The difficulty in quantifying catcher defense is due largely to the multifaceted nature of the position. Catchers form half of the pitching battery and field approximately 200 pitches in the span of a nine-inning game, and have to prevent passed balls and wild pitches. But they also play the field, catching pop ups, protecting against the bunt and throwing out runners on the base paths. FanGraphs lists four skill sets that are central to the defensive value of a catcher: arm strength and accuracy, pitch blocking ability, pitch framing ability and pitch selection. Defensively, at least, catcher is arguably the most unique position on the diamond.

Despite the difficulty in producing a single defensive analysis of catchers, several metrics do exist to evaluate individual skill sets behind the plate. Of course, catchers compile a fielding percentage like any other position player. But the drawbacks of fielding percentage as a statistic — namely its reliance on the observations of the official scorer — are well established. As for more revealing statistics, two in particular provide a deeper understanding of a catcher’s ability than any other currently devised metric: rSB and RPP.

Calculated by the Fielding Bible, Stolen Base Runs Saved runs above average (rSB) measures a catcher’s arm strength and accuracy. Essentially, this statistic attempts to calculate how many runs a catcher saves by throwing out base stealers and preventing stolen base attempts. The metric has two layers. The first establishes that a catcher with a stronger arm will be able to throw out more base stealers than a catcher with a weak throwing arm. This sets up the second layer — intimidation. A base runner facing a catcher with a strong arm will be less likely to attempt to steal a base for fear of being thrown out. The usefulness of rSB can be seen in a comparison of Mike Piazza and Yadier Molina of the St. Louis Cardinals. Piazza had a notoriously weak throwing arm, as demonstrated by his -22 rSB. Piazza’s arm was so weak that it cost his team 22 runs in the field from 2003-2006.[1] Meanwhile, Molina’s arm is widely regarded as one of the strongest in baseball. From his rookie season in 2004 to today, rSB shows that Molina has saved 52 runs in the field — purely from his control of the running game.

Bojan Koprivica’s RPP attempts to measure a catcher’s value in runs prevented due to his ability to block pitches. Pitch blocking can provide value to a team both immediately and over the course of an inning. A blocked wild pitch can prevent a runner on third base from scoring, or it can prevent a runner on first from advancing into scoring position. Regardless, the ability to block pitches has clear value. To again use Yadier Molina as an example, according to RPP, his pitch blocking ability has saved the Cardinals 27.9 runs in the field from 2008-2013.[2] But’s that benefit comes from a catcher’s ability to block pitches. What about his inability? According to RPP, that can hurt a team. To pick on another offense-first catcher, Jarrod Saltalamacchia cost his team 4.4 runs from 2008-2013 due to his inability to block pitches at the plate.

While they measure two different aspects of a catcher’s defensive ability, rSB and RPP combine to form the fielding element of WAR for catchers. According to Fangraphs, “Scores above zero are good, and those below zero are bad.” Specifically, scores of five and above are “excellent,” while scores of -5 and below are “awful.” Essentially, Yadier Molina is a really good catcher, while Mike Piazza and Jarrod Saltalamacchia are really bad catchers.

RPP and rSB are useful metrics for understanding the defensive value of catchers. However, certain skill sets remain unquantifiable. Specifically, there are no statistics for pitch calling and pitch framing. The ability to call a good game and the ability to have balls called strikes both have great value. And indeed, some catchers are regarded as good pitch callers, while others are adept at the subtle glove movements used to frame pitches as strikes. Unfortunately, there are currently too many factors affecting game calling and likely too many pitches thrown to establish useful metrics for either category.

The issue of game calling has particular relevance due to its role in statistics for pitchers. While metrics like FIP attempt to remove defensive variables from a pitcher’s performance, they do not account for the catcher’s role in calling pitches. Say a batter hits a home run. Was the home run due to poor pitch execution by the pitcher? Poor pitch selection by the pitcher? Or was it poor pitch selection by the catcher? While pitch calling in general might currently elude sabermetricians, the relatively modest number of home runs in a season could provide an interesting case study.

Despite the significant advancements in evaluating their defense, quantifying the defensive values of catchers remains problematic. However, the growing acceptance of the value of defense, combined with greater access to game data suggest that new metrics will continue to demystify catcher defense. In the meantime, one thing remains certain — Yadier Molina is a damned good catcher.

[1] The first year FanGraphs began recording rSB and the last year Piazza appeared at catcher.

[2] 2008 being the first year the statistic was recorded on FanGraphs.


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