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.

Kumar Rocker Velocity by Game
Date Opponent Line Pitches FB Avg FB Peak P51+ FB Avg P51+ FB Peak
February 22 Wright State 4 IP, 1 H, 0 R, 3 BB, 8 K 67 96 99 95 97
February 28 Georgia State 5 IP, 3 H, 0 R, 3 BB, 6 K 84 94 98 94 97
March 6 Illinois-Chicago 6 IP, 2 H, 1 R, 1 BB, 11 K 86 96 98 95 97
March 13 Oklahoma State 8 IP, 2 H, 0 R, 1 BB, 9 K 103 NA NA NA NA
March 19 South Carolina 8 IP, 3 H, 2 R, 2 BB, 14 K 116 94 96 94 96
March 25 Missouri 6 IP, 5 H, 2 R, 2 BB, 5 K 92 90 92 90 92
April 1 Louisiana State 6 IP, 4 H, 1 R, 0 BB, 8 K 89 91 94 90 93
April 8 Georgia 5 IP, 7 H, 6 R, 2 BB, 12 K 100 92 96 91 95
April 16 Tennessee 7 IP, 2 H, 0 R, 1 BB, 8 K 97 95 98 94 97
April 23 Mississippi State 9 IP, 3 H, 2 R, 0 BB, 8 K 109 94 98 93 96
April 30 Florida 5 IP, 4 H, 2 R, 4 BB, 8 K 95 92 96 92 96
May 7 Alabama 5 IP, 6 H, 6 R, 5 BB, 13 K 110 92 96 91 96
May 14 Mississippi 7 IP, 5 H, 3 R, 1 BB, 8 K 99 93 95 93 95
SOURCE: Synergy Sports

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.

Kevin Goldstein is a National Writer at FanGraphs.

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We miss Ross Ohlendorf
2 years ago

Not that it’s ever a bad thing, but is this the worse year to have the 1-1 pick in recent memory?

2 years ago

This year reminds me a bit of 2017. There are five players who would be Top 5 picks in most years but not any generational talents.

Then again, I’m not sure that it’s that obvious there is an elite, #1, slam-dunk, generation-changing prospect in most drafts. Adley Rutschman, obviously; Gerrit Cole, too. Maybe Casey Mize and Dansby Swanson…maybe. I know lots of people thought that Torkelson was in that category but I’m not exactly buying it. Some people were saying that about Byron Buxton but he didn’t go #1 (and in hindsight, it was obvious the opinions of who the top pick was in that draft varied a lot).

Smiling Politely
2 years ago
Reply to  sadtrombone

You know the ’17 draft was brutal when not even the Dodgers can play any of their guys selected from that year

2 years ago

I don’t think this draft is anywhere near as bad as 2017; the 2017 draft’s talent level dropped over dramatically at Pick #6. But the Top 5 is reminiscent of the Top 5 that year.

2 years ago

Zach Pop was drafted by the Dodgers (he’s in the majors with the Marlins now)

There’s several of them at AAA this year, but most of them aren’t with the Dodgers, and the ones who is wasn’t for a while (Reks). It seems like they were very aggressive using this class in trades (Betts deal, Machado deal, Reks going away for Dozier and back for Maeda, Pop, etc)

It’s sure not the 2016 Dodgers draft, but few drafts are.

2 years ago

I’m a biased Phillies fan but the Moniak draft (2016) has been brutal.

2 years ago
Reply to  snood

On the other side of the coin something like 12 or 13 players from the Dodgers’ 2016 draft have appeared in MLB.

Gavin Lux
Will Smith
Jordan Sheffield (Rockies)
Mitch White
Dustin May
DJ Peters
Devin Smeltzer (Twins)
Luke Raley
Andre Scrubb (Astros)
Tony Gonsolin
Dean Kremer (Orioles)
Zach McKinstry

8 of their top 10 picks are currently on MLB rosters: the last two are Errol Robinson (AAA-Reds) and their 10th rounder, a senior-sign for $2500 (they spent all their bonus pool on the other guys). Of course, 9th round pick Gonsolin was also a $2500 senior sign (they went $500k above slot for May)

Really got to be a contender for one of the best drafts in modern history.