Willi Castro is Flailing Against Left-Handed Pitching, Hampering Twins Lineup

On Monday night against the Royals, Willi Castro had another signature moment in his impressive, burgeoning career. Down by a run, Castro launched a homer off right-hander Brady Singer, giving the Twins a two-run lead and pushing the team on toward an 8-3 win. In Wednesday’s loss, Castro fared less well, with two strikeouts and an extremely soft line out to lefty Cole Ragans.

An 0-for-3 day against one of the best starters in the game (plus a popout against reliever Lucas Erceg) would usually be nothing to worry about. However, the bad day fits into an alarming trend for Castro since the end of June. He became an All-Star, in part, due to his switch-hitting prowess--especially his ability to punish left-handed pitching. But since the start of July, he has become an automatic out for southpaws.

The numbers should be ringing alarms within the Twins front office. Castro dropped from a stellar 202 WRC+ against left-handed pitching in the first half to a mind-bogglingly low -49 WRC+. He is 2-for-38, with only two walks and 10 strikeouts. I cannot emphasize this enough: From the beginning of the season through June, Castro was the best hitter against left-handed pitching on the team. Now, he sits dead last. Lefty pitching usually means small sample sizes, but it is quite impossible to look at these numbers and not see someone who has lost themselves at the plate.

Castro’s usefulness to the Twins remains substantial. He fills multiple shoes throughout the defense, and plays practically every day. Crucially, during this disastrous period, he still holds a more-than-healthy 120 wRC+ against right-handed pitching. But if the team’s health improves, it will be hard to imagine a role for him with a lefty on the mound; he could be relegated to platoon duty.

What is behind this brutal drop? Simply put, lefty pitchers are finding out where to put fastballs against him. Castro has yet to hit a single fastball by a left-handed pitcher for a hit, and you can see here that they’ve finally found his weak spot from the right side of the plate, where Castro is letting balls go by and putting himself in weak counts. That often means he forces himself into swinging at anything coming by, in the hope of finding contact.

Although it looks much more red all over in his early months, what the data is showing is how Castro had no particular spot that he would hold back. Now it’s clear what to do as a southpaw: start on the outside part of the plate and get him quickly into pitcher-friendly counts.

This remains a fascinating wrinkle in Castro’s game. After all, the reason Castro has been a recipient of a staggering number of Hit-By-Pitches is because of right-handed pitchers trying to play him inside. But comparatively, left-handed pitchers are working him away, where he gets overeager. His whiff rate against lefties is just a hair under 50%, meaning half the time he swings, he just flat-out misses the ball. Left-handed pitchers are simply putting the ball on the outside edge, where he cannot seem to find it. Castro's best spots are more inside the plate; he finds himself reaching out for balls on the outside and making weak contact.

One theory was floated by broadcaster Cory Provus during a game this week. Provus reminded viewers that Castro originally had a poor start to the season, but as he moved around to each position, he quickly found his swing. Since the beginning of July, Castro has almost entirely been relegated to the infield (despite the needs in the outfield), and since Brooks Lee’s injury, he's remained at shortstop. It would be hard to believe this kind of change in defensive responsibilities could make a difference, especially when Castro remains an essential hitter against right-handed pitching, but perhaps the repetitive motion of throwing strongly with his right side across his body over to first base is adding a strain. Or, perhaps more conspiratorially, Castro is nursing an injury unbeknownst to the clubhouse that has affected his right side.

Let's assume, for a moment, that he's healthy. That certainly doesn't preclude the rest of Provus's theory. One very difficult thing about being a switch-hitter is that one must maintain two different swings, which can be exhausting and extra difficult. Paradoxically, though, you're two different hitters, but you're still only one person. A change from nomadic defensive responsibilities to playing the same place every day means changing one's mindset to half of one's job, and it's plausible that that would lead a switch-hitter into some trouble with the highly plastic task of maintaining two distinct offensive approaches.

Hurt or healthy, what is notable is how controlled Castro's recent swings are--but not always in a good way. When batting as a lefty, Castro can look a bit all over the place, leaning in and out from the plate and losing his balance in the process. But look at this pitch against Cubs reliever Drew Smyly on an 0-2 count, in an area where Castro once punished the ball:

The swing seems almost casual, and the lack of power is quite obvious. Look at how his hands seem to drop immediately after making contact. It is, simply put, not a Big Swing. Look at a recent left-handed swing where Castro finds a hanging cutter and see the difference:  You can see the power on display. The whole body leans into the swing. Something different is happening when Castro swings from the right.

Castro’s days as a starter against southpaws feel numbered, if things do not turn around. While Rocco Baldelli has kept him hitting first against right-handed pitching, he found himself in the six-hole against Ragans Wednesday. If Correa returns soon, I might imagine him dropping down even below catchers Ryan Jeffers and Christian Vázquez. Nobody wants to see it, but moves might become necessary faster than expected.

What do you think is behind Castro’s plummeting numbers? Sound off in the comments.