If you manage to stay out of the comments section of online stories about Twins catcher Jason Castro’s season-ending knee surgery, you will come to the sane conclusion that yes, this is a loss for the Twins. Even if he wasn’t hitting well this season, Castro has a good amount of value as a receiver.
That said, many of his contributions come in the more subtle part of being a good receiver of pitchers — both calling a good game and, even more, being a good “pitch framer.”
If you’ve grown weary of that phrase and/or don’t completely understand it, you’re not alone. But essentially it means a catcher is good at making sure strikes are actually called strikes — and that he is also good at taking the occasional borderline pitch that’s an inch or two outside the zone and making it look like a strike so that it is called that way.
A catcher who is good at this might get a couple more called strikes per game than the average catcher, which could steal critical strikeouts or prevent hitters from getting into favorable counts.
Castro, for the most part, was good at this. But if the Twins’ chief objective in getting by for the rest of the year without Castro is having someone who can duplicate that strength, they are well-positioned.
In fact, one could even make the argument that journeyman veteran backup Bobby Wilson — the 35-year-old who is signed for the veteran minimum ($545,000) and was added to the roster when Castro was injured — is even better at Castro’s signature skill than is Castro, who is on the second year of a three-year, $24.5 million deal.
Using Stat Corner’s data on catchers’ pitch-framing skills going back to 2010 — Castro’s rookie year in Houston and pretty much the start of Wilson’s MLB career as well — we find that Castro has a much larger sample size.
He’s had 51,237 opportunities to receive a pitch at which a batter did not swing, and he’s plus-210 in terms of expected strike calls above average. So his reputation for being good at that is earned.
Wilson, though, in 14,941 opportunities, is plus-120. Castro has more by sheer number, but if Wilson maintained that rate and had the same number of chances as Castro, his expected strike calls would be plus-411 — almost twice as many as Castro.
From the data, we can draw three potential conclusions:
1) Wilson is a better pitch framer than Castro. That’s the simple way to look at it based on all the data.
2) If we isolate just on data since 2014, as both catchers have matured, they would be about even. Castro is plus-230 since then, while Wilson is plus-47, but if Wilson had played as much as Castro and maintained his rate they would be about the same. And there you’d find that Castro’s hitting (.697 career OPS) makes him the far superior catcher over Wilson (.587 career OPS).
3) If we look at the year-by-year data, we find that there is some volatility. Castro was great from 2014-16 with the Astros, but was minus-73 with the Twins last year. But this year he was back near the top at plus-42 before the injury. Was he suddenly really bad at something he had been very good at, or are there other factors (the pitchers throwing to him, even the way the data is tracked itself) that makes it too “noisy” to be reliable? FanGraphs took a look at this idea last year and concluded the data is getting “increasingly random.”
That would be good news for the Twins in at least one regard: Mitch Garver, the young and better hitting half of the team’s catching duo this season, is not deemed to be good at framing. He’s minus-29 this year — very close to the bottom among MLB catchers. He’s deemed to be costing pitchers a couple strikes per game, while Wilson and Castro were both gaining a couple.
If the data is not meaningful, it’s all the more reason to play Garver — the much better hitter of the two.
That said, pitch-framing data at least appears to be somewhat relevant even if we shouldn’t become too reliant on pitch-framing stats. And if it’s something the Twins — and Twins pitchers — liked about Castro, it’s something they will continue to like as long as Wilson is filling in for him.