Chicago Cubs Sign Free-Agent Lefty Reliever Caleb Thielbar to One-Year Deal

It's not the kind of move fans were hoping for. It's not a move that charts any kind of new course in the Cubs' bullpen construction. The team announced a one-year, big-league deal with lefty reliever Caleb Thielbar on Tuesday afternoon, just ahead of the end of the year. The signing fortifies the team's middle relief corps, but only in a very modest way. Thielbar, who will turn 38 years old next month, has pitched in parts of eight big-league seasons over the last 12 years. 

Thielbar first made it to MLB with his hometown team, the Twins, after a sojourn in independent ball, in the middle of last decade. Then (after a fairly forgettable first turn in the bigs as a relatively soft tosser and mediocre middle reliever), he resurrected his career amid the COVID pandemic. He's been a much better, more modern and impressive reliever the second time around, sometimes earning high-leverage work as a lefty who can get out batters on either side of the plate. 

His highest average fastball velocity of any season in his career came this season, at age 37. That's the kind of career arc it's been, for a pitcher who first made his mark by having a famously, almost secretly high-spin slow curve. It was a cousin of Rich Hill's skyscraping overhand curve, back at a time when Statcast was just beginning to proliferate and spin rates seemed like magical keys to understanding everything. That didn't keep Thielbar in the big leagues all that long, though.

What brought him back was hard work to become a harder thrower, to the point where his heater has sat around 93 miles per hour and gotten up to the higher side of 95 more than a few times over the last two years. He pairs that four-seamer with a sweeper and that curveball, and has run respectably even splits for most of this second act of his career. He posted an ugly 5.32 ERA in 2024, but that belies a much stronger performance on a fundamental level.

He had to work through a miniature career crisis, as he scuffled badly early in the season and (as people will do) many mused about whether his fairytale career was nearing its unhappy ever-after. He slid across to the third-base side of the rubber at midseason, though, and several things clicked. Thielbar has evolved and survived several changes of style and shape of pitches in his career; this was just the latest. It's well-documented here, but much of the good stuff from Twins Daily author John Foley is behind a paywall, exclusive to our Twins Daily Caretakers. I can share this much of it for you, though:

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Those shifts make good sense, because Thielbar’s breaking pitches had been grading out much better in the public pitch quality models than his four-seam fastball:

That usage tweak has been helpful to his results, as seen in the tables above. However, it doesn’t fully explain why the pitch quality scores of each of his pitch types have increased significantly, despite the same general physical characteristics of the pitches.

Take a closer look through the tables above. The bottom table shows the numbers are almost uniformly (and dramatically) better. And, importantly, Thielbar’s whiffs are back, especially with his fastball and curveball.

In short, Thielbar changed his alignment and made a slight modification to his mechanics, and it paid off handsomely. He health with injury problems in 2023 and 2024, and will probably be an occasional health question mark in 2025. That's how being an aging pitcher getting every ounce of power from a medium-sized body goes. Still, he strikes out more hitters than his fastball velocity might imply that he would, and when he's got his secondary offerings locked in, he also limits walks well. He's a superb complementary lefty, and we can safely assume he came fairly cheap.

Both the curve and the sweeper can be plus offerings when he has them ranged correctly, and he mostly has. The sweeper, especially, can be devastating, even against righties, because it has fairly big, two-plane shape coming from a deceptive delivery. Thielbar's extension isn't elite, but he seems to fly down the mound at hitters, and it adds to the efficacy of both his breaking pitches. The fastball sits in the movement dead zone a bit, but I wouldn't be surprised if the Cubs address that by adding a cutter to his mix as a wrinkle. He's tinkered with one before, and is well-suited to it. The Cubs are a good environment in which to tease that particular adjustment out a bit more.

This move will be good for clubhouse vibes and for playing matchups in middle relief. Thielbar has more upside than most pitchers of his age or with his track record; he just can't be your best or second-best reliever throughout a season. He's a great story, a Minnesota native who made good with the home team—twice. 

The only bad news here is that Thielbar does take up a 40-man roster spot, the only open one the Cubs had at the time of the signing. They can open up more spots in any number of ways, with several fungible players still clinging to the fringes of that reserve list. For instance, he's a marked improvement upon Rob Zastryzny, whatever good feelings spelling 'Zastryzny' right might bring because of his associations with the 2016 Cubs. Zastryzny is out of options, so he was no more flexible a piece than Thielbar, and Thielbar is demonstrably better.

Again, you figure the money involved here is limited. This is the first time Thielbar has ever reached traditional free agency, thanks to his adventurous career arc, and he has never made more than the $3.2 million he pulled down via arbitration last year. Presumably, since the surface-level numbers weren't great and he's both old and lacking a top-flight fastball, he'll make around that figure for the 2025 Cubs. As such, the move is fine. It's uninspiring, but it will make the team's bullpen incrementally deeper and better, and doesn't foreclose any of the other moves we assume they're entertaining. It does, however, seem to crowd the bullpen a bit, and make it harder to envision the higher-end relief acquisition that still seems essential.