His top-line seasonal numbers obscure how good the lefty has been out of the ‘pen
By now, you’re all probably familiar with Minnesota native Caleb Thielbar’s improbable baseball story. A decent reliever for some bad Twins teams from 2013 to 2015, Thielbar improbably made it back to the majors in 2020, some five-plus years after his last major league appearance.
After reinventing himself through training at Driveline to become a modern and reliable ‘pen contributor the past two seasons (3.00 ERA/3.20 FIP in 84 IP/76 appearances), Thielbar was a near-lock to make the 2022 club out of Spring Training and figured to be one of the more trusted members of the Twins’ reconfigured bullpen.
Then the season started.
Over Thielbar’s first four appearances, he allowed 9 of the 16 batters he faced to reach base via five hits and four walks. None of the seven outs he did record came on a strikeout and just four of the 72 pitches Thielbar threw in those outings drew a swing and a miss. In the end, seven of those nine runners came around to score, leaving the lefty with an ERA of 23.63 and a FIP of 7.64.
That terrible start might have left more than a few Twins fans wondering if this feel-good story had run its course. (Our game thread comments suggest so!)
Then something clicked. Thielbar’s fifth outing on April 20 was scoreless and included two strikeouts. His next was the same, but with three punchies. Because progress is never linear, Thielbar had a two-run hiccup on April 26, but quickly bounced back with another scoreless, three strikeout outing to close out the season’s first month. May and early June have continued along those lines.
Now, through games played on June 13, Thielbar’s ERA still sits at a seemingly bloated 5.24. But that obscures the fact that he’s been the Twins’ best reliever this side of Jhoan Duran (and one of the better relievers in all of baseball) for the past eight weeks.
I’ve written before that stats like ERA and Saves are incomplete measures for evaluating relievers. Instead, fielding independent pitching, win probability added, and leverage are better ways to characterize how a reliever is throwing.
By those, Thielbar has been excellent, as the numbers and ranks shown below illustrate:
WPA divided by leverage index (WPA/LI) is also known as context-neutral wins and is a way to see how much win probability a player added, regardless of the situation. Sometimes relievers, by nature of the pressure-packed situations in which they are used, can rack up a lot of WPA simply because they happened to pitch more often when the game was on the line, not necessarily because they pitched well. So, while Thielbar ranks 4th among Twins relievers for the leverage of the situations he’s worked (behind Duran, Emilio Pagán, and Joe Smith), he’s delivered the most context-neutral win probability of any Minnesota reliever.
Of course, it is part and parcel in the life of a reliever that a few bad outings can wreck the seasonal stat line and make it an all-year endeavor to whittle those numbers down to something respectable. In Thielbar’s case, the top-line numbers still look pretty rough, but there are many indicators in his underlying data that he is far from finished and that his recent run of solid work can continue. For starters, just look at all the red on his Statcast summary:
Further, the 2.18 point gap between Thielbar’s seasonal ERA and FIP, while steadily closing with each good outing, is still the 24th-largest of all 296 pitchers to have thrown at least ten relief innings this season.
Opponents have hit .235 against him for the season, but have done so while averaging a very weak 83.4 mph exit velocity that ranks in the 99th percentile across all pitchers. That weak contact has somehow resulted in a .333 batting average on balls in play. Given the soft contact, Thielbar’s expected batting average and slugging percentage against from Statcast are just .203 and .352 and in the 92nd and 84th percentiles, respectively.
What’s more, Thielbar had also struck out 30.5% of the batters he has faced (a career-best) while averaging a career-high 92.4 mph on his four-seam fastball (up from 91.3 mph in 2021 and 89.8 mph in 2020) and 80.9 mph on his sweeping slider. That extra juice has come while the movement profile of those two pitches has moved in desirable ways. By Statcast’s measurements, Thielbar’s fastball is dropping less (12.3 inches vs. 13.5 inches last season) and is among the league’s best for vertical movement relative to its velocity.
His slider has a bit more horizontal sweep thanks to it also dropping less (39.7 inches vs. 41.2 inches) while maintaining significantly above average horizontal movement. And, he still has the big, slow curveball that he throws about a quarter of the time. That three-pitch combination makes him one of the few relief pitchers in the game (let alone a left-handed relief pitcher) that can offer three different pitches that each get swings and misses better than 25% of the time a batter goes after them.
By Stuff+, the comprehensive measure of pitch quality developed by Eno Sarris and Max Bray for The Athletic, Thielbar’s total arsenal has been about 5% better than the league average this season. That’s a noticeable improvement over last year when he finished almost right on the league average by the same measure.
You can see in the summary chart above that Thielbar’s 10.5% walk rate is only in the 23rd percentile. However, that mark is inflated by the four walks he issued in those first four April outings. Since April 20, Thielbar’s walk rate is 7.6%, just slightly better than his career mark of 8.2% and in line with last season’s 7.5%.
That is supported by all the underlying measures of a pitcher aggressively working ahead and throwing strikes, especially compared to those rough first few outings:
All of this is to say, don’t be fooled by his ERA. Caleb Thielbar has been excellent for the Twins this season. Given the challenges the Twins have faced on the pitching staff and the heavy workload that’s been asked of the bullpen, Thielbar’s effective work has been critical.
Beyond that, a credible argument can be made that this is the best version of him that we’ve ever seen. Going forward, with the quality of the stuff he has, his ability to miss bats to keep the ball out of play and limit hard contact when it is hit, and improved control to limit free bases, there are few reasons to doubt that he can keep this kind of performance up.