Kumar Rocker Is Finally Coming to the Majors

Yeah what the heck, let’s watch the super regional no-hitter again.

This is Kumar Rocker at his peak: A 19-strikeout no-hitter in the NCAA Tournament. (Also: Hey, look, it’s Joey Loperfido!) Watching that video, you’d get the notion that he ran up to the mound that night in Nashville and got the Duke lineup to swing at every single 59-foot slider he threw. You wouldn’t be too far off. Peak Rocker was one of my favorite college players ever, because he had everything you’d want from an athlete. He was big, he was physical, he was skilled. To watch him was to watch an excitable teenager (which he was) operate the body of a major league ace (which he had).

Pitchers like him come along only so often, guys who not only mow down college hitters but do it in a fashion that makes you wonder how even professionals will ever cope. Stephen Strasburg, Gerrit Cole, Carlos Rodón, Paul Skenes, and Rocker.

The straight line to the majors ended up not being so straight. There was COVID, and the emergence of Jack Leiter as the better Vanderbilt pitching prospect, and concerns about Rocker stagnating. After all, this was a kid who never should’ve made it to college in the first place, who more or less solved the game as freshman, winning a national championship and being named most outstanding player of the College World Series along the way.

Then Rocker got Brady Aiken’d by the Mets, spent a year in the wilderness of independent ball, then got drafted in the first round again, this time by the Rangers. The last time I saw Rocker pitch was in March 2023. I happened to be in Arizona for the World Baseball Classic, and tagged along with Eric Longenhagen to watch Jacob deGrom and Nathan Eovaldi make simultaneous minor league rehab starts on adjacent back fields at the Rangers’ facility in Surprise.

Rocker was starting yet another minor league spring training game, and the slider looked awesome. It bit and dove and tempted and deceived A-ball hitters, many of whom were frankly inferior to the competition Rocker had dominated in college. But that was the end of the good news. Rocker was only throwing in the low 90s, and could locate neither his fastball nor his slider. He looked broken. Two months later, Rocker went in for Tommy John surgery.

It’s easy to forget that annoying detail about can’t-miss prospects: They miss all the time. I started to worry that maybe Rocker would go down as a legendary college performer whose professional career was undone because it started three years later than it should have.

Not to worry. Rocker is making his major league debut tonight against the Mariners.

It’s a little belated — Rocker is almost 25 now — even though the Rangers didn’t have him waste a single pitch more than necessary in the minors. Since returning from Tommy John, Rocker has made just seven starts across Double- and Triple-A, totaling 29 2/3 innings. In that time, he’s allowed just 13 hits, three earned runs, and four walks while striking out 47.

Rocker’s two Triple-A starts got tracked and entered into the Baseball Savant database, and the results are illuminating. His four-seamer averages 98.1 mph and plays up to a maximum velocity of 99.9 mph. He’s also throwing a high-90s sinker and a low-90s changeup, both of which feature roughly 15 inches of arm-side movement. This highlight reel of Rocker’s first Triple-A start includes an audacious right-on-right changeup for a swinging strike.

That leaves the slider. It’s the pitch Rocker threw the most over those two outings, making up 55 of the 132 pitches he threw.

Now, a couple weeks ago, I was quite unkind to the slider as a class of pitch. After comparing other secondary offerings to precise, mature art implements, I said the slider was like a crayon.

Turns out some artists can do a lot with a box of crayons.

In those Triple-A starts, Rocker threw 55 sliders, as I said, and opponents swung 31 times. Eighteen of those 31 pitches were outside the strike zone, and 23 of those 31 swings ended in a whiff.

I don’t really know how to contextualize a 74.2% whiff rate, even in a two-start sample. Here’s the best I can do. The top whiff rate on any pitch in baseball this season, minimum 100 pitches, is Mark Leiter Jr.’s splitter, which generates a swing and miss 58.6% of the time. (Rocker truly can’t escape the Leiter family, even in random statistical comparisons.)

Obviously, a splitter is not a slider, and Triple-A is not the majors, but pitches with high whiff rates tend to be chase pitches — either the hitter swings and misses or lays off the pitch for a ball. Just looking at whether the pitch results in a strike, either by hitting the zone or generating a whiff, Rocker is ahead of the best swing-and-miss pitch in the league.

It’s basically unheard-of for a single pitch to generate a called-strike-plus-whiff rate over 50%. Anything over 40% is elite. According to Baseball Savant, only five pitches have been thrown 50 or more times in Triple-A this season and generated a CSW% of 50% or higher. One of them is Rocker’s slider. One of the others is Blake Snell’s curveball.

I’m trying very, very hard not to get back out over my skis with Rocker. There is basically zero track record of minor league success for him, and whatever his gifts may be, big league hitters are stronger, quicker, and smarter than anything Rocker has faced before. I don’t know if he can sustain the effort to throw the way he does for 90 pitches a game, once every five days. He’s had trouble keeping his mechanics together — a lot of the problems he faced both at Vanderbilt and early in his professional career had to do with letting his release point drop.

None of that is enough to dampen the excitement over what’s happening now. Rocker is making his major league debut, coming off the heels of a white-hot run through the upper minors, in which he was pumping upper-90s gas and throwing an unhittable breaking ball. This is an event I viewed as a virtual certainty from about April 2019 to June 2021, and had increasingly despaired of ever getting to witness in the three years that followed. You don’t want to miss it now that it’s happening for real.