Evaluating catcher defense has long been one of the banes of saberists everywhere. While there have been some strides in evaluating defense for position players — see: UZR, DRS – catchers are a separate world in and of themselves. There are a number of different defensive skills that catchers need to possess, and each of them has the potential ability to impact their overall value defensive: arm strength and accuracy, pitch blocking ability, pitch framing ability, and pitch selection.
At the moment, saberists have focused their research on the first three factors, as pitch selection is a tricky thing to isolate and does not reside solely in a catcher’s purview. You can currently find two the first two factors on FanGraphs: arm strength and accuracy, and pitch blocking ability.
rSB: Calculated by The Fielding Bible, Stolen Base Runs Saved measures how many “runs” a catcher contributes to their team by throwing out runners and preventing runners from attempting steals in the first place.
RPP: First calculated by Bojan Koprivica, Passed Pitch Runs (RPP) calculates the number of runs above / below average a catcher is at blocking pitches.
Both of these values are then added together, and account for the “Fielding” component in WAR for catchers.
Like all defensive stats, both rSB and RPP are centered around 0, meaning that a score of zero is considered league average. Scores above zero are good, and those below zero are bad.
Note: these values are for each stat separately. If you would like tiers for catcher defensive value in total, double the values of the above tiers in order to get a quick-and-dirty estimate.
Things to Remember:
● While FanGraphs does not yet account for pitch framing, Mike Fast has made some remarkable strides measuring a catcher’s pitch framing ability. If you’re interested, be sure to check out his research.
● Next to RPP, you will also see the stat Calculated Passed Pitches (CPP). This is another statistic derived from Bojan’s research, and it measures how many passed balls a catcher should have allowed based on his pitches seen.
Links for Further Reading: