Plenty of promise, but what role will he play in 2025?
2024 by the Numbers:
- Rating: 5.39
- 2024 Stats: 7 G, 28.1 IP, 3.81 ERA, 4.47 FIP, 1.376 WHIP, 111 ERA+, 0.3 bWAR, 0.1 fWAR
- Date of Birth: August 19, 2000
- 2024 Earnings: $740,000 (via Spotrac)
- 2025 Status: Pre-Arbitration, 2 minor league options
Introduction
There has been an interesting theme underlying the last several years of the Mike Hazen administration’s pitching staffs: high-upside arms squeezed between the rotation and the bullpen. Some of the recent victims of this trend include Bryce Jarvis, Drey Jameson, and Tommy Henry over just the last two-plus seasons. These are pitchers who have mostly (80% or more) been treated as starters in the minors and have enough of a pitching arsenal to find success, but do not have the experience or routine to be stretched into the rotation as a full-time member. To be fair, there have always been pitchers who are more truly starters but are either too inexperienced or there other, extant roster implications that keep them from being more than a spot starter. Even Hall of Famers like Jim Palmer and Pedro Martinez began their illustrious careers by working more out of the bullpen than in the rotation as a means for exposing them to both major league hitters and coaching. It now seems as if Yilber Diaz may be the latest casualty for the team as he cleanly split his very brief appearances between the rotation and bullpen.
Originally signed for a measly $10,000 out of Venezuela in the 2021 international signing period, the expectations for Diaz were somewhat muted as he didn’t appear in the Top 30 list for the D-Backs until last year. However, he turned some heads around that year by finishing with AA Amarillo and posting a 3.60 ERA in three starts to end the season. That kind of momentum can be fleeting, but it turned out the 23 year old was just getting started.
2024 Season
He began this season repeating the AA level, but quickly moved onward after posting some middling results including a 4.33 ERA and 1.241 WHIP in 11 starts, but those numbers are inflated by a clunker (1.2 IP, 8 ER, 4 H, 5 BB) to end his time in Amarillo. Prior to that nightmare, he had limited opponents to a .184 BAA and a 3.10 ERA, clearly showing some impressive growth and earning some additional trust from the development team. The youngster then moved onto Reno in mid-June and posted similar results – a .220 BAA, 3.27 ERA, and a 1.227 WHIP. Those results combined with Christian Mena’s demotion two days earlier earned Diaz his first call up in early July to face off against a stout Atlanta lineup at Chase Field. He absolutely shined by twirling a six-inning gem in which his only blemish was a solo homer to Austin Riley in the first inning. Unfortunately, he did look unsurprisingly raw at times – especially in an horrendous outing against the Royals when he was tagged with seven earned runs in just three innings. Thus, it was not a complete shock when he was sent back down to Reno when Slade Cecconi continued his yo-yo relationship with Reno in late July.
Once back in the batter-friendly confines of the Pacific Coast League, Diaz continued to post solid numbers (2.82 ERA, .262 BAA, and 1.166 WHIP) in several starts before starting to make a transition to the bullpen. After a pair of bullpen appearances with Reno, the D-Backs took advantage of the expanded rosters to recall him to the majors in a reliever role rather than in the rotation. He certainly seemed to embrace the change, mostly working as a long man or middle inning reliever, posting a 3.24 ERA, 1.566 WHIP, and .290 BAA. Overall, he ended the season with a 4.05 ERA as a starter in four starts and a 3.24 ERA as a reliever in a much smaller sample size.
2025 Outlook
If we look ahead, Diaz could be in a precarious limbo position. As it stands now, the rotation appears full with Zac Gallen, Merrill Kelly, Brandon Pfaadt, Eduardo Rodriguez, and Jordan Montgomery (not necessarily in that order) fully ensconced as starters. That would not appear to allow for Diaz to have a spot in the rotation, but it would be a Christmas baseball miracle if those five were to remain healthy for an entire season and not miss a single start. Clearly, the team will need other players to step up and start even if it’s on a temporary basis. But at the same time, there are obviously very different processes for preparation, training, and maintenance between the rotation and the bullpen. Diaz will need a defined role at some point in the season – regardless of the level at which he is doing it. The path of least resistance would likely be leaving the youngster at Reno as a starter and bringing him up if and when one of the aforementioned five either falter in their performance or their health. However, his arsenal – including a fastball that nearly touches triple digits, a wipeout slider, and an upper-70s knuckle curve – could play exceedingly well out of the bullpen and there isn’t a team in the majors that couldn’t use additional bullpen help. For whatever it’s worth, Fangraphs’ projections mostly sees him as a starter with decent results and over 100 IP in the bigs. If I had to guess, I would wager that Diaz will end up in some kind of Swiss Army-style role a la Bryce Jarvis where he might cover multiple innings if needed, maybe act as an opener on some occasions, and work as a higher leverage reliever in extreme cases. I also wouldn’t be shocked though either if Mike Hazen elected to move one of the five penciled starters (cough cough Montgomery) and roll the dice on some of the high-upside pitching prospects rotating through the back end of the rotation. Either way, I’m excited for more of whatever Diaz is cooking!