Seattle Mariners Struggle Against Rangers Prospect in Debut; Here's Why

Originally posted on Seattle Mariners on SI
By Teren Kowatsch | Last updated Sep 13, 2024 9:15 PM ET

SEATTLE — The Seattle Mariners didn't start their series against the Texas Rangers on a positive note.

Seattle lost 5-4 to Texas after leading 4-1 through six innings. The Mariners let up four unanswered runs to the Rangers through the seventh and eighth innings.

It wasn't a great day for Seattle. But it was an amazing day for rookie Texas starter Kumar Rocker.

Rocker, listed at 6-foot-5 and 245 pounds, made his major league debut on Thursday. The former Vanderbilt Commodore was ranked as the No. 2 Rangers prospect and the No. 95 prospect in all of baseball according to MLB Pipeline.

One Mariners fan in the audience at T-Mobile Park loudly exclaimed when the home team was at the plate: "He only has two pitches — fastball and slider."

That fan wasn't wrong. Rocker just threw a four-seam fastball and a slider according to Baseball Savant.

But what that fan failed to mention was Rocker's slider had incredible movement that generated unreal swings-and-misses. According to Rob Friedman, AKA Pitching Ninja, Rocker's slider generated 13 swings-and-misses. Rocker had a 40.5% whiff rate on the day according to Baseball Savant.

Kumar Rocker's 13 Swings and Misses on his Slider last night. pic.twitter.com/Eptk8ZoWYv
— Rob Friedman (@PitchingNinja) September 13, 2024

Rocker threw 74 pitches on Thursday. Forty-seven of those pitches were strikes (64%).

The movement on the slider took the pitch out of the zone several times, but that also didn't seem to matter. He had a 45.2% chase rate, also according to Baseball Savant.

Rocker pitched just four innings on Thursday but struck out seven batters while allowing one earned run on three hits. He also walked two batters.

Seattle has had to go against its fair share of "Mariner killers" over the past several seasons. Yordan Alvarez from the Houston Astros, Jo Adell from the Los Angeles Angels, etc.

But it looks like the Rangers found a starting pitcher that not only could be the latest in that aforementioned list, they found a starter that has the potential to be solid for many years to come.

Much to the chagrin of Seattle fans.

This article first appeared on Seattle Mariners on SI and was syndicated with permission.

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