Turn Up the Volume on DJ Herz

Spinning His Way to a Breakout

Jan 29, 2025

Introduction

With Spring Training quickly approaching, it feels like the right time to start planting my flag on players I think will excel during the upcoming season. One of these players is LHP DJ Herz of the Washington Nationals.

I must admit, when Herz was first called up this past summer, I was pessimistic. His BB% throughout his MiLB career were scarily high and his AAA Statcast metrics weren’t very encouraging as his tjStuff+ was below average and he struggled to generate chases.

However, there was a saving grace to his profile: his ability to generate whiffs and limit damage.

These aspects are a great foundation for any pitcher, but concerns about his command had many scouts insisting that his future was in the bullpen. After all, the 19.0 BB% he posted in AAA would likely not fly in MLB, and would definitely not be that of a starter.

Herz’s command issues stem from his release. He throws from a 3/4 slot with a whippy cross-body delivery. These mechanics are the main talking point for the pessimistic assessment of Herz’ command because they are difficult to replicate. However, the deception his release adds is a key building block to his success. His arm action is incredibly difficult for LHH to pick up on, and when he can locate his pitches, RHH have trouble getting a good read.

Rookie Rhythm

DJ Herz was effective in his rookie season, posting a 4.16 ERA and 3.71 FIP across 88.2 innings. Herz most notably kept his walk issues in check in the Majors with a 9.4 BB%.

So what changed?

Herz started filling the strike zone with his fastball! From AAA to MLB his fastball Zone% improved from 49.3% to a more average 55.0%, which fueled a substantial +6% and +18% increase in Strike% and First-Strike% respectively. Both his Zone% and First-Strike% were still below league average, but they were much more passable than his putrid AAA numbers.

Herz credits Adam Wright, the Nationals’ director of mental performance, for helping him lock in and calm down throughout a start. In a Washington Post article by Spencer Nusbaum, Herz stated:

“I like to work really fast. I like to move. I like to get the ball and get back on the mound, and it works sometimes. When things are going good, it works well. But other times, we’ve got to be conscious of: ‘Hey, we need to slow down. We just need to take a second, breathe, look at the clock, slow it down then get back into that groove.’ ”

Herz worked with Wright to slow down his pace and become more comfortable on the mound. These changes were immediately fruitful as he fired off a brilliant 13 K and 0 BB game in just the 3rd start of his career. With a clearer headspace and more time to prepare for each pitch, Herz’s command issues seemingly faded away which allowed his stuff to flourish.

Fastball Forte

The most impressive aspect of Herz’ results from 2024 was the elite Z-Whiff% of his fastball. I like using Fastball Z-Whiff% as a proxy for stuff because it explains if a fastball is effective at missing bats in the zone. A pitcher with elite Z-Whiff% is able to deceive batters on their most hittable pitches and also gives them room for error if they leave mistakes in the heart of the zone.

DJ Herz’s 26.1 Z-Whiff% on his Fastball ranked 4th amongst MLB starters, and was equally as productive against RHH and LHH which led to his fastball returning +9 Run Value according to Baseball Savant. He was pounding the zone with fastballs and missing bats at a phenomenal clip.

Herz’s delivery is a major reason why his fastball is such an effective whiff generator. His fastball sits at 92-94 MPH (a +2 MPH increase from AAA) with average iVB which he supplements with great extension. The pitch grades out at 100 tjStuff+, but its production is elevated given his deception.

Changeup Cadenza

Surprisingly, Herz’s best weapon isn’t even his fastball! Herz was lauded for his changeup which grades out as a 70 Grade offering according to Fangraphs. His changeup’s velocity and vertical separation from his fastball make it grade out well according to stuff models, and he pushes it to that elusive plus-plus status thanks to its deceptive tendencies. He throws the offering with identical arm speed as his fastball and its late break allows the pitch to drop under bats.

Herz interestingly used the offering behind in the count often, which isn’t too much of concern given its above average Zone%. However, the pitch plays off his fastball exceptionally well when he locates it in the bottom third. His command of the pitch was seemingly not consistent as it had a very wide spread in locations. A more refined feel for his changeup will lead to plenty more whiffs and chases down and away to RHH and will ensure that Herz can remain as a starter.

Its interaction with his fastball is more noticeable when you overlay the pitches. In this sequence against Ramon Laureno, Herz dishes a 0-1 fastball to the outer third which is subsequently fouled off by a late swing. Two pitches later Herz mimics his delivery while landing a changeup nearly a foot below the fastball. The pitches looked identical out of hand and midway through its flight which let Herz fool Laureno for the strikeout.

Deeper Discography

Herz supplements his strong fastball-changeup duo with a gyro-slider to give him a platoon neutral option to better tackle LHH. The pitch exhibits more cutter like movement due to its minimal glove-side action and less depth than a typical slider. He is not afraid to throw the offering in any count and it has done an effective job at limiting damage.

He also toyed with a knuckle-curve “deathball” which added depth and an additional velocity band to his arsenal. The offering readily missed bats in its minuscule sample last season. If he shows more consistency and reliability with the offering, it could equip him with a devastating put away pitch.

Sophomore Album

Herz enters the 2025 season in a battle for Washington’s #5 rotation spot with former starter Mike Soroka. Given Soroka’s success as a reliver, he may be utilized in a weekly “3-4 Inning” guy which would effectively make the Nationals have a 6-Man rotation. While this doesn’t bode well for Herz’ volume, it will ensure that he will get regular playing time.

On top of his playing time questions, the concerns about Herz’ command are still present. His BB% gradually increased as he entered September, but he avoided a total collapse as his K% stayed steady.

Young pitchers are difficult to project as most of the information we know about them is from their MiLB careers. In Herz’ case, some of the most popular projection systems (Steamer, ATC) are pessimistic about the improvements to his command as they project his walk rate to worsen to ~11.5 BB%. This is understandable as he registered a poor 15.4 BB% across 321.0 innings before astoundingly righting the ship in the Majors. These projection systems also anticipate a significant drop in his FIP from his solid 3.71 FIP to as far down as 4.30 FIP.

Overall, DJ Herz showed very encouraging strides in his strike throwing ability last season while missing bats at an elite rate in-zone with this fastball. He returned solid results in his rookie season without great production on his best pitches. Maintaining his improved BB% will be key to success in 2025, and if everything clicks, I expect Herz to shatter his underwhelming projections.

I will be bumping DJ Herz’ sophomore album, and I hope he drops some bangers!

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