Lucas Kelly — Mariners Prospect Profile
Mariners reliever, No. 16 in the September 2026 rankings. Scouting reports, development notes and outing-by-outing analysis from Jason A. Churchill.
Kelly projects to the majors as a middle arm with a chance to get outs late, especially versus right-handed batters. He offers velocity, deception, angles, and a plus slider, but he has to throw more strikes.
The stuff is not in question. Kelly struck out 37.6% of the batters he faced in 2026 with a 17.8% swinging-strike rate, and at High-A before the promotion it was 40.4% and 19.4%. Those are not middle-relief numbers. They are the numbers of a pitcher hitters cannot touch when he is around the zone.
His ERA finished at 4.64. His FIP finished at 3.09. That gap is not luck, and it is not defense. It is five nights.
Jason A. Churchill
Across 41 appearances Kelly allowed 28 earned runs. Fourteen of them — exactly half — came in five outings that covered 3.7 innings combined. Remove those five and the other 36 appearances produce a 2.49 ERA across 50.2 innings with a 40.6% strikeout rate and a 10.1% walk rate.
Here is the part that makes your closing line the whole story. Every one of those five outings featured multiple walks: two, one, two, four, two. He did not get hit hard in them. He stopped throwing strikes, and the innings came apart before he could finish them. Four times all season he failed to record three outs, and each of those was one of the five.
The rest of the time he was close to unhittable. Twenty-five of his 41 appearances were scoreless. Twenty-one of them included no walks at all.
And the trend is pointed the right way. His walk rate was 18.5% in a brief 2025 look at High-A, 14.9% at the same level in 2026, and 11.5% after moving up to Double-A. Sorted by date rather than level, it went from 16.5% across his first 20 appearances to 10.7% across his last 21. The thing he has to fix is the thing he spent the season fixing.
Jason A. Churchill
Jason A. Churchill
Jason A. Churchill
