Well, his walk rate and home run rate are both up. The good news is that his strikeout rate has improved from 25.5% in 2025 to 29.1% this season. Unfortunately, that has not been able to counteract the walk rate going from 5.9% to 11.8%, and even worse, his home runs per 9 innings going from 0.78 to 2.45. This has led his ERA to balloon from 2.64 to 4.56.
In digging into some of his underlying numbers, there were no immediate red flags:
- His velocity is actually up slightly on all his pitches
- His pitch movement has not changed significantly
- His pitch mix has included a few more sliders, but the OPS against is consistent across all of his pitches
My first suspicion was his ability to get his off-speed pitches into the strike zone.
Here is a breakdown of the strike percentage of his pitches:
| Year | K% FB | K% SL | K% CU |
|---|---|---|---|
| 2025 | 73.1% | 64.8% | 59.7% |
| 2026 | 71.1% | 67.1% | 55.9% |
It looks like he’s having a bit more trouble getting strikes from his Curveball, but he’s actually been better with his slider.
One outlier for 2026 appears to be hitters making contact against his curveball when it is in the strike zone.
In 2025, hitters only made contact on his curveball 75.9% of the time when swinging at it in the zone, but in 2026 that number is up to 95%. And the OPS against his curveball has gone up from .394 in 2025 to .746 this season. The barrel rate has gone from 3.0% to 8.3%. So when he gets the curveball in the zone, hitters appear to be looking for it.
The slider regression is not quite as bad, with the contact rate decreasing, but the OPS going from .445 to .734. And the barrel rate from 2.2% to 4.3%.
The fastball, despite having a touch more velocity and the same movement as 2025 is also getting barreled a lot more – from 11% to 23.3% – and he’s given up 4 home runs on fastballs.
Here are all the homers Thielbar has allowed:
- 4/10 vs the Pirates
Bryan Reynolds gets a curveball on the inner-half an hits it out to left. The only runs scored in the game
- 4/23 vs the Phillies
Adolis Garcia gets a game-tying home run on a high slider in the 9th. The Cubs won in extra innings.
- 6/3 vs the Athletics
Colby Thomas blasts a fastball over the heart of the plate to cut the Cubs lead to one (in a game they would lose)
- 6/6 vs the Giants
Rafael Devers hits a solo shot on a high-inside fastball in the 6th to give the Giants a 1-0 lead. The Cubs would win in extra innings.
- 6/15 versus the Rockies
Cole Carigg caught up to a high fastball, to give the Rockies a 4-2 lead. Fortunately, the Cubs came back to win.
- 7/8 vs the Orioles (1)
Colby Mayo hits a high fastball to cut the lead to 3.
- 7/8 vs the Orioles (2)
The next hitter, Tyler O’Neill hits a slider on the inner half to cut the lead to 2.
One thing I noticed in these at bats is that everything is middle and up. If you look at his Heat Map for this season there is a big red circle, right in the middle of the plate
Contrast that with 2025, and you can see that a larger group of pitches lower in the zone
Ultimately, if you combine the increased walk rate with the increased barrel rate, it seems like Thielbar has had issues with his command – leading to more baserunners and hard contact. Hitters have been able to look for one of his pitches, and square up ball in the upper part of the strike zone.
With his track record, this seems like a problem that can be corrected, which the Cubs are very much going to need with all of the injuries they’ve had.
Cubs in 7 
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