Jack Kochanowicz bursted onto the scene at the end of 2024 for the Angels posting a 3.99 ERA, 104 ERA+, 1.19 WHIP, and 3.8% BB%. He came up as a high groundball pitcher with the occasional strikeout. In 2025 he sports a 5.53 ERA, 74 ERA+, 1.59 WHIP, and 10.4% BB%, all well below what he did in 2024. On the surface we can see that his BB% went sky high, but what happened and who is the real Jack Kochanowicz? Is it the league catching up or is he doing something different?
First, we will look at the changes from BaseballSavant year over year.
FB velo, average exit velocity, chase rate, and hard-hit % were about the same year over year. However, whiff% (+5%), k% (+6%), BB% (+7%), barrel % (+4%) went up while GB% went down (-6%). So on the surface it appears more of a focus on swing and misses than groundballs, higher number of walks, and barrels. Interestingly, his xERA and xBA were around the same. Expected metrics are generally better because they account for randomness and luck, and it appears that maybe the 2025 version is more of who he is and he was lucky in 2024.
Let’s look deeper at the data.
First let’s look at pitch usage.
| Pitch | 2024 | 2025 | Change |
| 4-Seam Fastball | 6.1% | 18.4% | 12.3% |
| Changeup | 2.9% | 10.9% | 8.0% |
| Sinker | 72.6% | 47.8% | -24.8% |
| Slider | 14.1% | 16.3% | 2.2% |
| Sweeper | 4.3% | 6.5% | 2.2% |
Kochanowicz has gone away from the sinker with a higher reliance on the 4-seam fastball and changeup this season. His sinker has been hit harder this year, but his homerun rate has skyrocketed with less of them.
This leads to the question of is he attacking hitters differently? Now let’s look 1st pitch distribution to see if there is the same trend.
| 1st Pitch | 2024 | 2025 | Change |
| 4-Seam Fastball | 3.0% | 13.5% | 10.5% |
| Changeup | 0.4% | 2.1% | 1.7% |
| Sinker | 75.2% | 53.9% | -21.3% |
| Slider | 17.1% | 25.9% | 8.8% |
| Sweeper | 4.3% | 4.6% | 0.3% |
A lot more 4-seam fastball and slider usage first pitch and less sinkers. How about with 2-strikes?
| 2-strikes | 2024 | 2025 | Change |
| 4-Seam Fastball | 13.6% | 24.0% | 10.4% |
| Changeup | 8.2% | 17.6% | 9.5% |
| Sinker | 54.4% | 39.4% | -15.1% |
| Slider | 16.3% | 10.4% | -5.9% |
| Sweeper | 7.5% | 8.6% | 1.1% |
Less sinkers and sliders, but more 4-seam fastballs and changeups.
It is clear that the approach throughout the entire plate appearance has drastically shifted from a lot of sinkers to a combo of fastball and changeup. In 2024 he actually only threw 25 changeups! The sinker and slider have shown differing results the last two season.
Sinker
| Year | wOBA | xwOBA | Difference |
| 2025 | 0.360 | 0.349 | -0.011 |
| 2024 | 0.330 | 0.348 | 0.018 |
Slider
| Year | wOBA | xwOBA | Difference |
| 2025 | 0.483 | 0.445 | -0.038 |
| 2024 | 0.310 | 0.307 | -0.003 |
For the sinker, in 2024 his xwOBA was higher indicating a little luck but that has reversed in 2025 where it is the opposite indicating a little unlucky. Overall the xwOBA is about the same year over year. So his sinker is about the same quality as last season.
The wOBA and xwOBA for the slider were about the same, but the difference year over year has been significant. Looking beyond this, the spin rate is similar to 2024. Exit velocity on the slider is up +2 mph, whiff % up +3.4%, and launch angle down -5 degrees. What gives?
Let’s look at location
From an initial look it appears more sliders are in zone and middle-middle in 2025, but there are more sliders thrown in 2025. Time to isolate on just swings.
Looks like a bit more in the zone and closer to middle-middle.
The Angels broadcast talked about the sinker being up this year contributing to the use of the changeup more. Here is the plot of swings on the sinker.
To me, it looks like a similar distribution.
So who is Jack Kochanowicz? I think he is somewhere in the middle of 2024 & 2025 to date. Cheap answer I know, but he drastically changed his approach to hitters and his expected metrics about the same which shows similar quality of contact from the hitters. Also there is only a year and a half-ish of data on him. What is contributing to his higher ERA is his high walk %. Definitely not a pitching coach but based on the data he needs better command, to increase the sinker usage, and fix the slider location or use it less. He is a groundball pitcher who should use the Angels infield defense to his advantage and not worry as much about the strikeout.
It is fascinating to me how players can be so good for a time and then the numbers flip. Always been interested in what they are doing different and how can they get back to who they were. More of this similar analysis in the future!
Analytics In The Outfield 