The Best Pitching Matchups of the Week: April 19-25

With another full week of baseball on the horizon, let’s set our sights on three intriguing faceoffs. One is riddled with questions about each starter’s ability to become a true ace, another connects two former teammates who have each proven themselves as aces, and the final is between two fellas who haven’t proven much of anything yet this year.

Tuesday, April 20, 6:40 PM ET: Zac Gallen vs. Luis Castillo

For years, Gallen has embodied promise. He was, and in many ways still is, the physical form of “could be.” The Cardinals took him in the third round of the 2016 draft, and his 1.62 ERA and 2.17 FIP at High-A in 2017 showed quick returns on the their investment. Gallen made it all the way up to Triple-A by the end of the year, then was traded to Miami in December 2017 along with Sandy Alcantara and two other players in exchange for Marcell Ozuna.

When he debuted for the Marlins in 2019, the former Tar Heel struck out 43 hitters in 36.1 innings. He was traded again at the deadline that year, but this time in a one-for-one prospect swap, as Arizona gave up Jazz Chisholm, the team’s No. 1 prospect, to land Gallen’s services. Following a top 10 Cy Young finish in 2020, Gallen and his deadly curveball are looking to finally erase the “could be” from his profile.

A spring training batting practice mishap led to a hairline fracture in his arm that caused Gallen to miss the Diamondbacks’ first three series. When the 25-year-old eventually took his turn in the rotation on April 13 against the A’s, he looked as if he hadn’t missed a beat, striking out eight in four innings.

Zac Gallen, 94mph Paint. ??? pic.twitter.com/AWqEFSuLIu

— Rob Friedman (@PitchingNinja) April 13, 2021

Opposite Gallen on Tuesday, the Reds will turn to Castillo. Stuff has never been the issue for Cincinnati’s one-time All-Star; the trouble has been keeping that stuff from flying over the fence. Since 2018, only Kyle Gibson has a higher HR/FB ratio among pitchers who’ve completed at least 400 innings. Part of that surely has to do with Castillo pitching in Great American Ball Park’s cozy confines, but part of it is also because his fastball gets hit hard. Entering 2021, batters had slugged above .500 on Castillo’s four-seamer in each year of his career, with a collective wOBA north of .375. Compare that with his changeup, against which hitters have never cracked a .360 SLG or .280 wOBA in any year, and the problem becomes clearer.

Luis Castillo gets himself in a little jam…

Then unleashes changeups from hell, Ks two in a row, and savagely smiles as he walks off the field. pic.twitter.com/qt3RCjzIwJ

— Rob Friedman (@PitchingNinja) August 6, 2020

Will Gallen resemble an existing ace rather than one who may hypothetically arrive later on? On the other side, is Castillo’s fastball trustworthy enough to complement the wipeout change? Or will Arizona succeed with the gameplan that’s kept him out of pitching’s upper echelon: wait for the fastball, and swing hard in case you hit it?

Thursday, April 22, 10:10 PM ET: Yu Darvish vs. Walker Buehler

While the purpose of this column is to highlight fun pairings that wouldn’t otherwise jump out, there’s always room for a good ol’ fashioned marquee matchup. When the two starters play for the teams comprising baseball’s hottest rivalry, it becomes even harder to ignore.

Armed with one of the most diverse pitch mixes in the league, Darvish always has the capacity to shake things up. One of your seven pitches not doing what you want it to? Might as well shelve it in favor of another mind-bending offering. His latest trend is more fastballs and sliders with fewer cutters and sinkers. This plan has worked so far in his nascent San Diego career: He’s thrown 60 sliders as a Padre, and hitters have a put up a putrid .079 wOBA (.196 xWOBA) against it. The only person to get a hit on Darvish’s slider so far is none other than Madison Bumgarner.

Unlike Darvish, who specializes in deception and a deep reservoir of pitches, Buehler is all about country hard ball. Through his first three starts, his four-seam percentage has climbed above 60%, and none of his other four pitches come in above 20%. That’s nothing new: Since 2019, he is one of 26 starting pitchers with a four-seam fastball usage above 50%. And among starters who have thrown at least 1,000 fastballs during that span, Buehler ranks seventh in average velocity.

Darvish shoved for seven innings against the Dodgers in his last start, ringing up nine strikeouts and allowing just one hit. Buehler did not enjoy the same success when he faced the Padres earlier in that series, coughing up seven hits in six innings.

In Thursday night’s NL West rumble, Darvish’s matchups against Justin Turner bear monitoring. Turner’s not only been one of the best hitters of this young season, but he’s also run a .371 wOBA against sliders in the Statcast era, and since 2014, he’s got a .382 wOBA against all breaking pitches. When the Padres are up to bat, Tommy Pham and Manny Machado could be the antidote for Buehler’s fastball: Both players have a matching .425 wOBA on four-seamers in the Statcast era.

Friday, April 23, 8:15 PM ET: Sonny Gray vs. Kwang-Hyun Kim

Gray and Kim have combined for 7.1 innings in 2021, thanks to back ailments held them both out until April 17, when they both got their first action in shortened starts. Gray tossed 4.1 innings against Cleveland in his season debut, while Kim gutted through three innings against the Phillies.

In an NL Central that lacks a true juggernaut, Gray and Kim could be crucial elements for their respective clubs. The departures of Trevor Bauer and Anthony DeSclafani tightened the margins of error for the Reds in the rotation. Tyler Mahle’s 39.3 K% has fortified them thus far, but the return of vintage Gray could lift them even higher, especially if their blistering offensive start continues.

Gray has seen the Cardinals five times in his career and been tripped up by the same bugaboo every time: walks. He’s walked multiple batters in every game against St. Louis and also turned in one of the worst outings of his life the last time they squared off back on September 1, 2020, when he recorded just two outs, handed out three free passes, and gave up six earned runs. One thing that could ease the nerves is that Paul Goldschmidt, Yadier Molina, and Paul DeJong are a measly 2-for-26 off Gray with 10 punchouts.

Kim introduced himself to the major leagues as a closer. Landing with the Cards on a two-year, $8 million deal following 12 seasons in the KBO, Kim notched a save in his lone relief appearance before shifting to a starter’s role. That turned out to be a wise decision. As a member of Mike Shildt’s staff, Kim held opposing hitters to a .190/.255/.314 line with a .245 wOBA. Four of the nine outs he got in his 2021 debut came via the strikeout, all of which were on a biting slider that appears to be in midseason form.

The Korean lefty goes heavy on the fastball and slider, though he’ll use both a curveball and changeup about 10% of the time. He compensates for his lack of velocity — his fastball averaged 89.9 mph last year — by throwing his slider with great regularity. Against the Phillies, he threw 26 sliders and 32 heaters, an approach that he isn’t likely to deviate from against a Reds lineup that’s been obliterating everything fast. It will be interesting to see how long of a leash Gray and Kim are given as they ramp up their workload post-injury.

Under the Radar Matchup — Friday, April 23, 7:10 PM ET: Yusei Kikuchi vs. Martín Pérez

Kikuchi knows his situation. He’s surely aware of the $66 million club option the Mariners can exercise after this season, and that unless he shows the bat-missing prowess that made him the prize of NPB, the Mariners will likely decline that option. That makes each of his starts even more important, including his first in Fenway Park.

Pérez knows his situation too. After pitching for the 2020 Red Sox on a one-year contract, the veteran lefty took less money to come back to Boston this winter, stating that he feels “at home” there. Whether he expected the Red Sox to be a first-place team is another story, but now Pérez finds himself in a position of heightened importance. Chris Sale is still recovering from Tommy John surgery. Though it’s still very early, Garrett Richards’ strikeout rate is down, and Nick Pivetta is handing out too many walks. Pérez is an important part of Boston’s rotation, and he responded with five innings and three earned runs or fewer in his first two starts before running into a tough White Sox lineup on Sunday.

Friday’s tangle with the Mariners will also allow Pérez to renew his acquaintance with Kyle Seager. No hitter has faced Pérez more than Seager, and no pitcher has faced Seager more than Pérez.