On Eiberson Castellano and the Role No One Player Can Fill

Managers do their best with disaster prep, but when it comes to bullpen management, there’s no way to prepare for everything. There are going to be games where a starter can’t deliver innings. There will be times when a bullpen is stretched thin. There are extra-inning marathons, doubleheaders and mid-game weather delays that throw monkey wrenches into the works.

When worse comes to worst, the mop-up man saves the day. Well, it would be more accurate to say he saves the other arms. A mop-up man doesn’t often help his team win; he’s there to eat innings. In that sense, it’s easy to think anybody can be a mop-up man. To some degree, I suppose that’s true. If you're down by enough runs, even a position player can cover mop-up duty on the mound.

The challenge is less finding someone to fill the mop-up role, and more what to do with him after he’s provided his service. The options are usually either to basically play shorthanded in the bullpen for a few days or demote your mop-up man to call up a fresh arm. That being the case, it’s nearly impossible to have a mop-up man you can’t send down to the minors. This, of course, creates a big problem for the future of Eiberson Castellano as a Twin.

Castellano is a talented pitcher. He won the Phillies' Minor League Pitcher of the Year honors in 2024, before being selected by the Twins with the ninth pick in the Rule 5 draft. He must stick on the Twins' active roster, or be waived, and if he clears waivers, he has to be offered back to Philadelphia. Currently, mop-up duty is the only role he currently looks suited for in the majors.

So far this spring, Castellano has been awful more times than he’s been awesome. As he's a 23-year-old who hasn’t pitched above Double A, it should be little surprise that Castellano has run into some trouble. After a rough outing on Tuesday, his ERA is up to 9.35, to go with a 1.85 WHIP over 8 2/3 innings this spring. Still, with a four-seam fastball touching 97 mph a useful curveball and a changeup with a chance to be average, Castellano has the foundation of a big-league arsenal. He’s struck out 12 of the 44 batters he’s faced this spring (27.3%), despite struggling with his control and command.

The team has also made sure to give him some tough assignments, the better to evaluate him against high-level competition. By Baseball Reference's Opponent Quality metric (an important tool to account for the uneven levels of opponents a player sees in spring ball), Castellano's 7.5 is the median figure among the 19 Twins who have thrown at least five innings this year. That number signifies something between Double-A and Triple-A talent, so it's pushing him beyond his comfort zone. Jhoan Durán (7.4), Jorge Alcalá (7.1) and Chris Paddack (6.8) have all faced a lower level of competition than Castellano. 

This is exactly the kind of arm you’d love to be able to stash for a year and steal away from another org. It’s just not that easy. There are enough low-leverage opportunities; the challenge comes from the bigger picture of bullpen management. It's easy to say "just stick him in a mop-up role." But here's the thing: No single pitcher can cover that role for an entire season.

There are times when it’s necessary to churn and burn. Last season, there were 14 instances where a Twins reliever had to record more than six outs, meaning that pitcher was unavailable for the next day or three. In those situations, teams often show their appreciation for the effort by demoting that pitcher. 

One example from last year is when Pablo López could only cover four innings against the Tigers on April 12. That doesn’t sound like much of a doomsday scenario, but the Twins had a doubleheader the next day. The first game went 12 innings. They had no time to take a breath, as their next game was the following afternoon.

Over those two days, Cole Sands covered 2 1/3 innings in an outing, while both Michael Tonkin and Alcalá had two-inning appearances. Additionally, Kody Funderburk and Jay Jackson worked back-to-back days. That’s five of eight bullpen spots who were likely going to be unavailable the next day (if not multiple days). Tonkin was the victim in that instance. The Twins had just acquired him from the Mets on April 9, but they designated him for assignment on the April 13 because they needed a fresh arm.

There were other disaster scenarios last season, but we typically think of them coming later in the year. The early-season schedule includes more days off than usual, to accommodate potential weather postponements, but it doesn’t completely prevent bullpen management nightmares from popping up as early as mid-April.

I suppose it’s possible to lock Castellano into a low-leverage spot and view a few of the other bullpen arms as the mop-up, churn-and-burn guys. Alcalá, Louis Varland, Justin Topa and Funderburk all still have options, so they could be up-and-down guys, yo-yo'ing between Minneapolis and St. Paul. There are also a host of arms not currently on the 40-man roster who could be used in a pinch, as we see every year. Those names include Huascar Ynoa, Randy Dobnak, Scott Blewett, Ryan Jensen and Anthony Misiewicz, among others.

It seems like the amount of gymnastics it would require to keep Castellano on the roster would impact multiple other spots in the bullpen. It’s not impossible to keep him stashed away, but he may not be worth all the extra acrobatics. It's possible he'd break camp with the team and that Alcalá would start in St. Paul (since the latter can only be optioned now; he'll no longer be able to be farmed out once he accrues eight more days of big-league service), only to see a repeat of the Tonkin thing three weeks into the season: Castellano eats some innings, Alcalá comes up to refresh that spot on the roster, and Castellano hits the waiver wire, never to return.

Another option Twins Daily writer Cody Schoenmann explored is for the Twins to trade for Castellano, allowing him to be optioned to the minors, but at this time it seems like Philadelphia would have little reason to go that route. I’d guess the Phillies would prefer to see how things shake out, and are assuming there’s a pretty decent chance Castellano is returned to them in the end. (Besides, there are logistical hurdles there, too. Castellano would have to clear waivers before that kind of trade could be executed, even if it had been previously agreed upon.)

The Twins have been inactive in the Rule 5 Draft in recent years, so it was a surprise to see them make a selection. Though they were clearly enticed by Castellano’s upside, it would be an even bigger surprise if he actually stuck on the roster all season. Perhaps it’s best to return him to Philadelphia now and pivot to another plan that allows more flexibility in the bullpen.