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# Jackson Steensma — Mariners Prospect Profile
- URL: https://baseballthings.com/jackson-steensma-mariners-prospect-profile/
- Published: 2026-09-04T04:06:00.000Z
- Updated: 2026-09-29T06:58:49.000Z
- Description: Mariners right-hander, No. 19 in the September 2026 rankings. Scouting reports, development notes and start-by-start analysis from Jason A. Churchill.
- Author: Jason A. Churchill
- Tags: Jackson Steensma

Steensma flashed overpowering stuff in 2026, but an injury derailed his season and he hasn't had the fastball command since his return. It's mid-90s heat with life, and a breaking ball with good depth and shape. I project a good bullpen arm here, perhaps in the mold of a Trevor May.

The season line says 4.57 ERA with a 34.9% strikeout rate. It is describing two different pitchers, and the game log separates them cleanly.

Through May 10, across six appearances and 19 innings, Steensma struck out 43.9% of the batters he faced, walked 3.0%, allowed seven hits, and gave up zero home runs. That is a 1.42 ERA and a strikeout rate that would lead almost any league. The overpowering stuff you describe is not a projection — it happened, and it is on the record for six weeks.

[Prospect Rankings Update: Final update of 2026 boasts fresh Top 10As the final update until the offseason work starts to get you prepared for prospect season 2027, we have changes... most of those due to a larger group of prospects in the majors – and I don't…![](https://storage.ghost.io/c/f2/85/f285ce72-40e3-409f-ae3b-2ef371936c02/content/images/size/w256h256/2026/08/BT27Logo1024width--1-.png)Baseball ThingsJason A. Churchill![](https://storage.ghost.io/c/f2/85/f285ce72-40e3-409f-ae3b-2ef371936c02/content/images/2026/09/Prospect-Rankings-Update-rounded-transparent.png)](https://baseballthings.com/prospect-rankings-update-final-update-of-2026-boasts-fresh-top-10/)

Then he did not pitch again for 61 days.

From his return on July 10 through the end of the season, across nine appearances and 24.1 innings: a 29.4% strikeout rate, a 7.3% walk rate, 29 hits, and eight home runs. The ERA over that stretch was 7.03.

The home runs are the sharpest signal of the three. Zero in 19 innings before, eight in 24.1 after. His season HR/FB rate of 22.2% is entirely a post-return number, and it is the reason his FIP finished at 4.83 while his xFIP — which normalizes home runs — sat at 3.79\. The walk rate more than doubled, which matches what you're describing about the fastball command, but nothing moved as far as the damage on contact.

The durability question surrounds all of it. He relieved at Appalachian State in 2023, started and threw 67 innings in 2024, has no 2025 season at all, and threw 43.1 interrupted innings in 2026\. He has not completed a healthy full season since he was 20, and his longest outing this year was five innings.