The baseball community has been trying to understand the defensive value of catchers for some time now. Pitchers, coaches, and front-office types often espouse the value that a backstop brings to the table in running a pitching staff, but it's not something that we've been able to quantify. Without the ability to measure the value of the non-obvious things catchers did (or didn't) accomplish, opinions were split: some felt that it was unquantifiable and that those who thought of game-calling as more than a myth were wasting time, and others believed we just lacked the data to put our proverbial finger on it.
There's still a long way to go to nail down the exact value of what catchers do behind the plate besides the obvious -- throwing out runners, fielding pop-ups and the like -- but the sabermetric community is making significant progress. We've seen perceptions change since Keith Woolner, now with the Cleveland Indians but formerly of Baseball Prospectus, looked at Catcher ERA (CERA) in 1999 and concluded that there was no evidence of catchers influencing pitchers on a large scale. Woolner, ever the forward-thinker, left the door open for better data, though:
...if there is a true game-calling ability, it lies below the threshold of detection. There is no statistical evidence for a large game-calling ability, but that doesn't preclude that [sic] a small ability.
There are other places to look for a catcher's influence beyond the game-calling ability looked for in this study. A catcher might be able to impact the "clutch" performance of the pitcher, helping him focus in high leverage situations. Such a pitcher would surrender fewer runs than expected from his hits & walks allowed. A catcher who senses what his pitcher is throwing well might be more efficient in calling pitches, reducing the pitch count per batter, and thus allowing the starter to go deeper into the game and preserving the bullpen. Nothing in this study precludes any of the possibilities from being true, and this is a promising line for future investigation.
That "promising line for future investigation" is what researchers like Dan Turkenkopf, Mike Fast, Bojan Koprivica, and Max Marchi have worked on over the last few years. Turkenkopf opened the door to analyzing framing pitches -- something Woolner suggested almost 10 years earlier, while lacking the means -- with the use of advanced data at Beyond the Box Score in 2008. Turkenkopf's research couldn't have been further from Woolner's, as it suggested that catchers were earning wins above replacement on a massive scale behind the plate, to the point where he felt his numbers were on to something, but also off-base.
The range narrowed over time, with Bill Letson halving Turkenkopf's results through his own methods in 2010, and then Sean Smith, in the Hardball Times annual later the same year, saying almost the opposite of Woolner a decade before: "catchers have a significant impact on the performance of the pitchers they catch."
Mike Fast -- who, like Smith and Woolner, now works in a front office -- has worked extensively on catcher defense from multiple angles. In 2011, he explained where the "real" strike zone that umpires call is, and as a follow-up months later, released run values for catcher framing. In the results, pulled from 2007 through 2011, the recently-extended Jonathan Lucroy rated fourth in the majors at 38 runs saved -- that's another four wins added to his totals, and that's just from knowing where the right place for his glove to be was. Those 38 runs came from just two seasons, too, meaning Lucroy, per 120 games caught, was worth nearly 2.5 wins extra per year due to framing. His extension makes much more sense in that light then if you just looked at his basic defensive value at, say, Baseball Reference.
Framing isn't the only area in which catcher defense needed advancement. Koprivica focused on pitch blocking in an extensive study from last October. Koprivica's research was so detailed that he even took the time to figure out what the effect knuckleballs had the defensive value of pitch blocking, so we could all feel appropriately bad for Jarrod Saltalamacchia. The effects of the knuckler were so great on Salty's ability to block pitches that he might look like a completely different (and far more competent) defensive catcher by the numbers this year, sans Tim Wakefield.
Koprivica saw a spread of nearly a win between the best and worst at blocking pitches. Combine that with Fast pegging framing at about plus or minus two wins in either direction, and a picture is painted in which catchers are shown to be far more valuable than anyone imagined from a statistical point of view in the past. The thing is, that painting is just half finished, as Turkenkopf described to us:
Measuring game calling is probably the last big unknown, at least when it comes to the game on the field. To me, game calling will be the biggest single aspect of catcher defense, and also the hardest to isolate. Without it, we're probably 50-60% of the way to understanding.
Marchi has explored game calling extensively in his short time at Baseball Prospectus, and as Turkenkopf suggested, the numbers are staggering. Jose Molina, who the Rays signed this off-season, was often considered a positive on defense. The numbers available didn't back it up, though. The research of Marchi, meant to reflect everything a catcher can influence in a plate appearance, suggests that front offices knew what they were doing employing him anyway: from 2008 through 2011, Molina was 103 runs better than expected. That's 10 wins in four years, and in over 10,000 fewer plate appearances fewer than the next-ranked A.J. Pierzynski, who came in at 82 runs. Jason Varitek, whose critics often pointed to the idea of his game calling being important enough to keep him around as misguided, ranked fifth in this stretch -- even with his declining bat and inability to throw out runners, he was a highly-productive backstop in his backup role.
Back in 1999, had Molina been around for more than just 10 games to that point, he would have been derided by the findings in Woolner's look at catcher defense. There just wasn't enough data out there to measure what needed to be measured, though, and advancements like PITCHf/x have helped to change that the last few years. While the work of Marchi, Fast, Koprivica, and others is far from over even with the help of PITCHf/x, we're much closer to understanding what catcher defense is all about. The Brewers, Rays, and others, to their credit and benefit, are already listening.