Castillo Gets the Call, Herget Gets the Door—The Mets Keep Spinning the Lefty Wheel

In their ongoing quest to patch the bullpen with duct tape and divine intervention, the New York Mets acquired 29-year-old left-hander José Castillo from the Arizona Diamondbacks in exchange for cash considerations.(Which, depending on the Mets' current budget, may or may not include loose change found in Steve Cohen’s sofa in his luxury box.) To make room on the 40-man roster, the Mets designated right-hander Kevin Herget for assignment-though if you blinked, you might've missed his entire Mets tenure. More on that later.

Castillo’s final appearance with Arizona may offer a clue as to why he was suddenly available: in a May 11 outing against the Dodgers, the southpaw somehow managed to commit three balks in a single game. Whether that was a mechanical glitch, or a mental lapse, remains unclear—but it certainly didn’t help his standing in Arizona.

Castillo is a 6’6” southpaw from Venezuela who made his MLB debut back in 2018 with the Padres and promptly turned heads with a 3.29 ERA and a WHIP that made fantasy owners weep with joy (0.91). In his very first outing on June 2, 2018, he came out of the bullpen and faced the heart of the Reds’ order—Joey Votto, Eugenio Suárez, and Adam Duvall—and struck out all three on swinging strikeouts. It was a dazzling, electric entrance that hinted at long-term dominance. Unfortunately, that rookie promise has since taken a scenic tour through the orthopedic wing of every medical facility this side of Dr. James Andrews. An ACL tear, a rotator cuff strain, a fractured finger—if there’s a body part, Castillo’s probably iced it.

Still, the Mets see potential in Castillo’s stuff, and the acquisition fits a clear organizational need. After losing both Danny Young and A.J. Minter to likely season-ending injuries, and with Brooks Raley still on the comeback trail, the Mets are desperate for left-handed help, and Castillo fits the bill: he’s breathing, throws lefty, and owns a pair of spikes. Genesis Cabrera, called up earlier this month, has performed well—pitching five innings of one-run ball over four appearances—but he's currently the only left-handed reliever in manager Carlos Mendoza’s bullpen.

Castillo is out of minor league options, meaning the Mets will need to keep him on the MLB roster or risk losing him via waivers. Dedniel Núñez, who still has options remaining, is the most likely candidate to be sent down once Castillo joins the active roster.

From a pitch data perspective, there's plenty for Mets pitching coach Jeremy Hefner and the club’s analytics-driven Pitching Lab to work with. Castillo leans heavily on a mid-80s slider and a 93-mph sinker. His slider, while not a big swing-and-miss pitch, has exceptional depth and late movement. His sinker, meanwhile, generates a high number of whiffs and shows strong downward action with above-average velocity. He’s also got a sneaky four-seamer that rides like a wiffle ball on the right day. Problem is, he sometimes pitches like he’s blindfolded.

In terms of Statcast metrics for 2025, Castillo’s xERA sits at 5.20 with a .274 expected batting average against. He’s struggled with command, as evidenced by his 9.7% walk rate, and his 12.0% whiff rate and 9.7% strikeout rate are below average. That said, he also induces ground balls at a 52% clip and has shown flashes of dominance at various points in his minor league and winter ball stints. His hard-hit rate (40%) and average exit velocity allowed (89.3 mph) suggest he’s not getting routinely crushed—leaving the door open for improvement with better sequencing and location.

Castillo’s baseball passport is full. Originally signed by the Rays in 2012, he’s pitched for San Diego, bounced through El Paso, Jacksonville, Reno, and—my personal favorite—Magallanes of the Venezuelan Winter League, where he posted a sharp 2.28 ERA last offseason. You’ve got to admire the guy’s persistence. He’s a walking billboard for arm care and Advil, but he keeps showing up.

Herget, meanwhile, exits the Mets’ 40-man after a brief stint. The 34-year-old journeyman was claimed off waivers from Milwaukee this past offseason and made just one appearance with New York, allowing two runs in one inning. He has pitched decently in Triple-A Syracuse, with a 2.87 ERA over 15.2 innings, though his strikeout-to-walk ratio has not impressed.

Castillo is now the second lefty reliever the Mets have added in the past eight days. On May 7, the club signed Colin Poche, recently designated for assignment by the Nationals. Poche has pitched just 1.1 innings in two games at Syracuse, struggling with command. But like Castillo, Poche represents a lottery ticket in the Mets' quest to find a serviceable left-handed arm.

In a bullpen where Cabrera is the lone lefty, and with Raley inching closer to a return, the Mets hope that Castillo—armed with a bat-missing sinker and slider with bite—can rediscover some of the promise he flashed back in 2018. Whether this proves to be a shrewd low-risk addition or another injury footnote in Castillo’s checkered career remains to be seen. If Castillo recaptures that rookie-year form, it’s a steal. If not? At least the Mets didn’t give up a prospect—or even a ShackBurger with fries.