The Astros Reunite With Old Friend Jason Castro

As the most physically demanding position on the diamond, catcher is fundamentally different than the other non-pitching positions. Combine the need for frequent rest and the higher likelihood of injury, and every team is always in search of more catcher depth. There’s a corollary to that, though: because catching exacts such a toll on the body, few catchers are truly standout stars in the same way that infielders and outfielders are. As an idle example, four catchers were worth 3 WAR or more in 2019, and 66 non-catcher position players crested that mark.

Why bring up this fact? Part of the reason is that it’s interesting to me, and I get to pick what I write about most of the time. The bigger part, though, is that I don’t always get to pick what I write about, and this one happens to be a fortuitous combination of the two: the Astros signed Jason Castro to a two-year, $7 million dollar deal with incentives that could tack on $2 million, and somebody needs to write it up.

At first glance, Castro is exactly the kind of catcher that teams always need: he may not be an All-Star (though he was in 2013), but he’s someone you can count on to punch the clock roughly every other day, delivering enough receiving, enough hitting, and enough being-there-ness to fill roughly half of a catcher platoon. Deals like this are evergreen — heck, Martín Maldonado signed roughly the same deal in Houston last year, and he’ll be Castro’s platoon partner. That said, Castro carries a few interesting notes that give him a chance to be more than just another faceless backstop.

First and foremost, Castro is a lefty. That’s not exactly breaking news — stop the presses, I watched a Jason Castro at-bat and found something new — but it’s indisputably valuable. There simply aren’t many left-handed catchers, even if you count switch hitters; lefties made 1,399 plate appearances at catcher in 2020, as compared to 5,272 right-handed plate appearances. That’s a 21% share of PAs, as compared to a 43% share for lefties in the league as a whole.

For the Astros, that means more games where they snatch a small but meaningful platoon advantage. Garrett Stubbs saw limited action in 2020 as a lefty (10 plate appearances), but for the most part, the team used Dustin Garneau and Maldonado in tandem. Neither are fearsome hitters, and they fare even worse against same-handed pitching; Maldonado is a career 72 wRC+ hitter against righties (82 against lefties), and while Garneau doesn’t have enough career playing time to say much about his splits, the odds aren’t high that he’s a better hitter against same-handed pitchers.

Castro is an abysmal hitter against lefties — in 727 plate appearances, he’s hit .195/.262/.291, good for a 53 wRC+. Against righties, he’s been good — .242/.328/.421, a 105 wRC+. Platoon splits take forever to stabilize, and it’s unlikely that Castro is that much better against righties, but even if you regress his splits heavily to the mean, he’s a useful hitter against righties and a husk of himself against lefties.

Because of that, Castro is best suited as a backup or tandem starter who can hit the bench against lefties. He’s also 33, and hasn’t carried a full workload at catcher since 2017. Even then, he only made it to 407 plate appearances; he topped 500 only once, in 2014. Again, though — it’s hard to carry a full workload as a catcher. Maldonado has never topped 500 plate appearances. Houston needs to get 650-700 plate appearances out of catcher, and combining two part-timers will let them hit that mark without unduly stretching either.

Castro’s calling card is his defense. He’s unlikely to replicate his ludicrous success from the end of his career with the Astros — he was 16.1 framing runs above average in 2016, the third-best mark in the game — but he’s been above average as a receiver in every season since 2013, when he revamped his catching style, and there’s little reason to think that he’ll suddenly lose that skill in 2021.

That alone would likely be worth the price of admission. If Castro combines an indifferent bat — we project him for a 79 wRC+ — with the level of defense we’ve become accustomed to, he and Maldonado will combine to form a league-average platoon. The Astros don’t need much production out of their catcher to make things work — mostly, they’re looking to avoid a black hole at any one spot while basking in the glory of Alex Bregman, Carlos Correa, and a host of other talented offensive players.

If the Astros knew they were getting exactly that Castro, they’d definitely make this deal. If you want to dream a little bit, though, you can certainly do it. After a wasted 2018 season, Castro put up a resurgent 103 wRC+ in 2019. It was also a shortened season — only 275 plate appearances — but he popped 13 homers in that time, by far the highest home run rate of his career.

Underneath the hood, Castro’s season looked even better. Put simply, he just started hitting the crap out of the ball. Let’s set a baseline first. From 2015 to 2018, he hit 34% of his batted balls 95 mph or harder, exactly league average. He barreled balls up at an average rate as well, and put a roughly average amount in the air. Combine that with his 30% strikeout rate, and you get a bad but playable hitter.

In 2019, that all changed. His hard-hit rate jumped to 47%. He barreled up 15.9% of his batted balls, nearly double his previous career high. In only 275 plate appearances, his 24 barrels set a new career high. He had that 103 wRC+, so it’s not like he was suddenly Mike Trout, but his expected stats showed far better — he managed a .368 xwOBA and a ludicrous .506 xwOBACON — expected production on contact.

As Alex Fast pointed out, that production continued in 2020. You can more or less throw out 92 plate appearances of results — a lot of weird things can happen in less than 100 trips to the plate. From a quality of contact perspective, though, Castro picked up where he left off, with a 14.9% barrel rate and career-high 55.3% hard hit rate. In addition, he set a new high for maximum exit velocity — topping his previous career high from 2019.

What led to this newfound pop? I’m still searching for an answer. It doesn’t appear to be a massive swing overhaul. Take a look at some solid contact from the 2018 season:

If you care, that one ended in a double. Here’s one from 2020:

That one was an out, albeit at the center field warning track. In terms of his swing, however, I can’t see much change. His front leg timing mechanism looks slightly different, but that’s hardly enough to explain Castro suddenly turning into a barrel monster.

It doesn’t appear to be a pitch selection issue, either. Castro just put up his lowest swing rate on pitches over the heart of the plate in 2020, and his 2019 was right on his career average. He swung at fewer fastballs than ever before, and naturally enough, set a career low in swing rate on fastballs thrown over the heart of the plate.

For now, I think we can file this one under interesting but as-yet unexplained. Castro showed a new skill in 2020, one that raises the prospect of a better-than-expected year with the bat. Will he do it again in 2021? He might! Treating this as predictive is a stretch, but it’s certainly something to keep an eye on.

The bottom line on this deal, though, is that Castro doesn’t need to deliver on this promise of power to make Houston happy with their signing. Competent veteran backstops are always in vogue, and the price is certainly right. If Castro comes out mashing next year, it won’t be out of nowhere. If he fades back to his bad-bat good-glove baseline (the most likely outcome in my opinion), well, at least he’ll always have 2019.