The Kumar Rocker Velocity Roller Coaster

The best word to describe how teams are approaching the 2021 draft might be “uneasy.” Teams lean hard on things like the Cape Cod League and summer high school showcases, which the industry lost in 2020 due to the pandemic. Track records of performance are hard to come by because of it (as well as other factors), and teams are desperate for anything resembling a sure thing.

Entering the season, Vanderbilt right-hander Kumar Rocker looked like one of these few sure things. A highly regarded prep arm out of Georgia in 2018, he might have slipped into the first round that year had he not made it abundantly clear that without an elite bonus offer, he had every intention of honoring his college commitment. He’s succeeded since arriving in Nashville, stepping right into the weekend rotation and throwing a no-hitter in Super Regional Play as a freshman. With athletic bloodlines and the much-desired combination of above-average stuff and command, Rocker entered the season as a strong candidate to be selected by the Pirates with the No. 1 pick come July.

He’s certainly held up his end on a performance level. Through 13 starts for the Commodores, he’s struck out 118 over 81 innings and allowed just 47 hits and 25 walks. But on a stuff level, it’s been a different story, as the average firmness of Rocker’s fastball has ranged by as much as six miles per hour on average from one start to the next. He is still expected to be a top-five pick at minimum, and that 1–1 slot is in play for him as well, but for teams looking for consistency, the varying fastball is a bit troubling. For teams looking for answer as to his ability to handle a pro workload, it’s even more so.

Rocker came out with the best velocity of his career in his first start of the season, averaging 96 mph with his fastball and touching 99. He averaged 94–96 over his next two starts and touched 98, but the first big drop occurred following a 116-pitch outing on March 19 against South Carolina. Seven days after that, I got a text message from a scout: “Are you watching Rocker?” I switched his start on and saw him sitting at 90–91 all of a sudden. And these were not the 87–91 cutters he’s added to his repertoire; these were four-seam fastballs.

Rocker topped out at 92 mph in that game and slowly got the velo back from there, as this chart of his game-by-game velocities shows. The P51+ column shows his velocity after 50 pitches, which has encouragingly been at the rate one would expect as opposed to significant drop-offs.

As you can see, the oomph on his fastball took a dip again after throwing 109 pitches, his second-highest total of the season at the time on April 23, and it’s now settled in at a consistent low-90s, touching 95–96. Evaluators would be somewhat comforted if this recent three-start run represented the real normal, as while he’s below his early-season velocity spike, he’s at least recovered from the disturbing mid-season dip and returned to his historical norms.

We didn’t see these kind of wild velocity swings out of Rocker as a freshman, when he averaged 93 mph with a best bolt of 98. In only three 2020 starts, Rocker was regularly 94–96, so he’s throwing as hard as expected in aggregate, but the up-and-down nature of his fastball has created some questions as teams start to organize for their initial draft meetings.

It’s important to note that velocity isn’t everything. With an altered arm slot from previous years, Rocker’s fastball shape is better than ever, and he continues to command the pitch well. The fastball also is far from his best pitch, as over 70% of his strikeouts in 2021 have come on breaking balls. But a Kumar Rocker who sits 90–92 versus one who sits 92–94 and one who sits 94–96 are three very different players. The first one is a late first-round talent; the last one stays in the corner of the Pirates’ board among the special magnets being considered for the first pick in the draft. And thanks to Rocker’s inconsistency and some recent sub-par (for him) showings by Jack Leiter (along with a skipped start two weekends ago), that first pick remains wide open, with high school shortstops Jordan Lawlar and Marcelo Mayer entering into the pool for Pittsburgh’s consideration along with Louisville catcher Henry Davis.

Rocker has just one regular-season start left in his college career, coming this Friday against Kentucky, but as one of the best teams in college baseball, Vanderbilt is expected to have a long postseason run. That should provide teams with a handful of additional looks to get more comfortable with what is currently an uncomfortable evaluation of one of the top pitchers in the draft … depending on what day you see him.