Last year was a banner year in the area of catcher-defense research. At Baseball Prospectus, Mike Fast unveiled a groundbreaking study on pitch-framing. The unsurprising part is that he found that pitch-framing is a skill. The surprising part is that he was able to study it so thoroughly, and that for some guys it can make an enormous difference in their defensive value. Not coincidentally, Fast was recently hired to work for the Astros.
Not one month later, at The Hardball Times, Bojan Koprivica published a groundbreaking study on pitch-blocking. This study was also exceptionally well done, and almost impossibly detailed. You can read over the entire method if you like. Or you can do what I did and skip to the tables while assuming that the method is sound. "Why would anyone take that much time to publish a flawed study?" I rationalized to myself. In my defense, the method includes this image:
I don't have to verify how the hamburger was made. I just want to buy and eat the hamburger. :(
Anyway, the study revealed some very interesting information. Why am I bringing this up now, if the study was published in October? Because FanGraphs is now tracking pitch-blocking data for catchers, based on Koprivica's method. Now we can know everything we wanted to know about pitch-blocking performance, going back to 2008. It doesn't extend earlier than that because the method relies on PITCHf/x, and PITCHf/x wasn't in place before.
Who shows up as the most effective pitch-blocker since 2008? Humberto Quintero, who is a catcher you might not have even heard of before, depending on your favorite team and how much attention you pay. Quintero's played for the Astros, and while the man hasn't hit, he's saved approximately 5.6 runs per 120 games blocking pitches. It stands to reason that a catcher who plays without hitting probably makes a positive contribution in the field. Quintero is followed by Yadier Molina (no surprise), Matt Wieters, and Brian McCann. Good pitch-blockers, the lot of them.
As for the least effective pitch-blockers since 2008, we're looking at Rob Johnson, with Jorge Posada a distant second and Miguel Olivo a closer third. That thing I said above about catchers playing without hitting -- it doesn't apply to Johnson, who doesn't seem to do anything particularly well. He doesn't block pitches well. Mike Fast found he doesn't frame pitches well. He definitely doesn't hit well. He doesn't have a great arm. No idea what the deal is with Rob Johnson.
Breaking away from individuals, Cardinals catchers have saved approximately 21.7 runs with their pitch-blocking since 2008. Mariners catchers, on the other hand, have been 27.6 runs below average in the same department. That's a difference between extremes of 49.3 runs in four seasons, which works out to about five wins. Pitch-blocking is not the most critical baseball skill in the world, but it absolutely does make a difference.
I'll leave you to explore the numbers further on your own. You're looking for RPP, which you'll find in the advanced catcher fielding section of the stat pages. Note that RPP is a counting stat, and not a rate stat. Go ahead, have some fun. While pitch-blocking is only one of a catcher's several responsibilities, it's fantastic to have a clearer picture of who does it well, and who does it less well.