Can the Twins Get Caleb Thielbar Right Again?

Caleb Thielbar has been a mainstay on the Minnesota Twins bullpen since 2020. His journey to the majors and his improbable return makes him one of the most unique Twins in the last decade. Thanks to a 3.21 ERA, a 1.13 WHIP with a 30 percent strikeout rate, and a 30.2 percent strikeout clip from 2020 to 2023, Thielbar has been the most productive pitcher in Minnesota’s bullpen. He’s recorded a 3.1 fWAR, which ranks higher than Jhoan Duran, Griffin Jax, and Taylor Rogers in that span.

But Thielbar has had a forgettable 2024 campaign. He started the season on the injured list with a hamstring strain, and Thielbar has been inconsistent since making his debut this year on April 14. His 5.79 ERA and 1.76 WHIP would be career worsts for the southpaw. Thielbar has already allowed 4 home runs in only 23.1 innings and is on pace to allow a career-high in longballs.

Once a high-leverage arm, the Twins have relegated Thielbar to mop-up duty to build his confidence. Injuries have also started to pile up for the 37-year-old. He missed time twice last season due to oblique injuries and only pitched in 36 games in 2023. If his production doesn’t improve soon, the Twins might not have room for Thielbar in the bullpen with the trade deadline and a playoff push looming. However, with the help of Driveline, the Twins have fixed Thielbar recently. Now they have to do it again.

After finishing his collegiate career with South Dakota State, the Milwaukee Brewers took Thielbar in the 18th round of the 2009 draft. However, they released him, and the Randolph High School graduate pitched for the St. Paul Saints when they were in an independent team before working his way to the big leagues with the Twins from 2013 to 2015 seasons.

Thielbar held his own in his first stint with the Twins during the Terry Ryan era. During his first three years in Minnesota, he threw 98.1 innings and had a 2.74 ERA and a 1.11 WHIP. He also had a 19.9 percent strikeout rate with a .219 opponent batting average. Those are productive numbers on the surface. However, he generally had low-leverage outings with a 0.66 average leverage index (0.85pLI is league average). Thielbar had a 5.40 ERA in 2015, beginning a five-year major-league hiatus.

Thielbar also spent the 2016 and 2017 seasons in independent ball with the Saints. Following the 2019 season, Thielbar retired and wrote scouting reports for the Augustana University baseball team. After a stop at Driveline, Thielbar bumped his velocity from an 89.9 MPH average in 2015 to a 91.9 MPH average in 2020.

Under Derek Falvey, the Twins saw his strides and convinced him to delay his coaching career and give pro ball another shot. They built off what Driveline was doing, encouraging Thielbar to develop his slider. Pair that with his development of a looping 12-6 curveball that messes with hitters’ eye line, and it became his best pitch to finish off an at-bat with a 22.6 strikeout percentage from 2020 to 2024.

Like most relievers, Thielbar and the Twins have been tinkering with various pitch mixes over the last five seasons. In 2020, Minnesota trimmed down his pitch arsenal from five to four pitches, ditching the sinker that he had when pitching for the Ryan-era Twins. Thielbar also stopped throwing his slider and replaced it with a changeup in 2021, then reversed that pitch selection last season. In 2024, Thielbar threw only three pitches: his 4-seam fastball, sweeper, and curveball.

Thielbar’s run of success has been fascinating because a first glance at his underlying numbers doesn’t suggest he’s on a dominant run. His 86.8 MPH average exit velocity sits just below the league average of 88.5 MPH, and his 9.3 percent barrel rate is worse than the 7 percent league average. Fastball velocity improved to 91.9 MPH but is still slower than the 93.7 MPH league average in fastball velocity.

Thielbar had generated just enough spin to make it tough for hitters to time up. However, things haven’t gone as planned this season. The fastball was once Thielbar’s best pitch and is now his least productive pitch. He has a -5 run value and a .340 opponent batting average against the 4-seam in 2024. Part of the reason why Thielbar’s 4-seamer is so poor is his career-worst 11.5 percent walk rate. Teams are spitting at his curveball and sweeper, which allows them to focus solely on timing up the fastball.

It’s common for a pitcher to make adjustments throughout their career. What will be difficult for Thielbar will be trying to adjust during the season with limited opportunities in games, especially this late in the year. Driveline is an offseason fix, not an in-season option. Pounding the strike zone is an easy start to bring down the walk rate and theoretically bring down the number of baserunners he has to deal with in an inning.

Thielbar must also make his fastball more productive by generating more swings and misses. If he can do that, success from his secondary pitches will follow. Opposing lineups must respect his offspeed pitches when they can’t just zone in on hitting the fastball. The other option is to lean into his curveball and sweeper entirely and drastically tone down his fastball usage.

In that case, he would frequently throw junk pitches like Sergio Romo. While it will never blow by hitters, they still can’t square it up. The only caveat is that Thielbar’s sweeper (-1 pitch value) and curveball (-2 value) have been negative pitches this season. However, his fastball is at a -5 run value, so it might still be the better option.

Caleb Thielbar has run into trouble in his career and has always found a way to pick himself back up or reinvent himself to keep his big-league dreams alive. The Twins built him up to become a successful big-league reliever again in the last four seasons. Now faced with another rough patch, Thielbar must bounce back with his fastball leading the way.