Texas Rangers' Kumar Rocker Racks Up Whiffs at Historic Rate in MLB Debut

Kumar Rocker dominated the Seattle Mariners' lineup with his slider on Thursday, setting the stage for the Texas Rangers to come away with a win in his first MLB appearance.

Sep 12, 2024; Seattle, Washington, USA; Texas Rangers starting pitcher Kumar Rocker (80) pitches to the Seattle Mariners during the first inning at T-Mobile Park. / Steven Bisig-Imagn Images

For as many hoops as he had to jump through before reaching the big leagues, Kumar Rocker did not disappoint in his debut on Thursday.

The Texas Rangers right-hander went 4.0 innings deep against the Seattle Mariners, allowing just three hits, two walks and one earned run. Rocker, the No. 1 pitcher and No. 2 prospect in Texas' farm system, also struck out seven Seattle batters and made history along the way.

Rocker got 13 swings and misses on his slider alone. According to MLB.com's Sarah Langs, that is tied for the third-most whiffs on a single pitch type by a pitcher in their MLB debut since the pitch-tracking era began in 2008.

Freddy Peralta owns the record, forcing 18 swings and misses on his four-seam fastball on May 13, 2018. Alex Colome and his changeup rank second with 14 whiffs back on May 30, 2013.

Tied in third alongside Rocker is George Kirby, who forced 13 swings and misses with his four-seamer when he debuted on May 8, 2022.

most swings & misses on single pitch type by a pitcher in his MLB debut, pitch-tracking era (2008):

5/13/18 Freddy Peralta, 4sm: 18
5/30/13 Alex Colome, change: 14
Today Kumar Rocker, slider: 13
5/8/22 George Kirby, 4sm: 13 https://t.co/vDJK8SlBjh

— Sarah Langs (@SlangsOnSports) September 13, 2024

Considering he can hit 97 miles per hour with both his four-seam fastball and sinker, Rocker has already shown that he has a dangerous enough arsenal to make the leap to the big leagues. He boasted a 1.96 ERA, 0.791 WHIP and 13.5 strikeouts per nine innings in the minors this season, and now he has a 2.25 ERA, 1.250 WHIP and 15.8 strikeouts per nine innings in the majors.

Rocker, once a first round pick by the New York Mets, has undergone shoulder surgery and Tommy John surgery since leaving Vanderbilt in 2021. He has worked his way back into shape and then some, as his slider is tracking to be one of the most untouchable pitches in baseball.

Should he remain in the Rangers' rotation down the stretch, Rocker could make two more appearances here in 2024. He and fellow Vanderbilt alum Jack Leiter are likely to return as key pieces on Texas' pitching staff in 2025, but it remains to be seen which veterans between Max Scherzer, Jacob deGrom, Nathan Eovaldi and Andrew Heaney will be there to fill out the group around them.

DeGrom, like Rocker before him, will make his season debut on Friday having also undergone Tommy John surgery in 2023. First pitch is slated for 10:10 p.m. ET.

Scherzer will be coming off the injured list to start against the Mariners on Saturday, with the contest scheduled to get underway at 9:40 p.m. ET.

Follow Fastball On SI on social media

Continue to follow our Fastball On SI coverage on social media by liking us on Facebook and by following us on Twitter @FastballFN.

You can also follow Sam Connon on Twitter @SamConnon.