The New Look Diamondbacks Bullpen Has Become a Team Strength

To say that the Arizona Diamondbacks have generally had a tough time piecing together a good, consistent bullpen during the Mike Hazen and Torey Lovullo era is a fair statement. In most seasons the team has ranked in the lower half of Major League Baseball in bullpen value rankings.

The exception to that was 2017, the first year under the current regime, when they ranked 13th. Since then, the track record has been spotty at best with an average ranking of 25th between 2018-2024.

Through the first 16 games of the 2025 season, however, the bullpen has shown vast improvement over last year and previous years. The team reliever ERA and FIP (Fielding Independent Pitching) have dropped over a run from last year, and the ranking has improved to 10th so far.

"We haven't had many hiccups down there," Lovullo said. They've been lights out. It's been the most stable part of the ball club when you break it down."

See table below.

Arizona Diamondbacks Reliever ERA, FIP and WAR with Rank | Jack Sommers

Stat notes:

FIP is a metric that takes into account just those things most under a pitcher's control, namely walks, strikeouts, and home runs allowed. Batted balls in play, and thus defense, are completely stripped out of this metric.

Fangraphs WAR for pitchers is based on the FIP metric, but also takes the leverage a pitcher was used in into account.

Improvement Tied to Velocity Increase

The clear and identifiable reason for the improvement from the current iteration of the bullpen is increased two-seam and four-seam fastball velocity. That is directly correlated to more strikeouts, fewer balls in play, and fewer hits.

But it's not only about velocity, of course. They're throwing strikes and not walking batters. That combination is lethal to hitters, as can be seen in the table below.

Arizona Diamondbacks Reliever Fastball Velocity and Ranks | Jack Sommers

So far in the small sample size that is the 2025 season, the team ranking in velocity and strikeouts has leapt into the top 10 in baseball. Relative reliever velocity in 2020 was also ranked ninth, and strikeouts were up, too, but so were walks, by a great deal. The current walk rate is less than half the year before.

In years past, the D-backs simply did not prioritize adding velocity to the bullpen, and ultimately ended up behind the curve. To be fair, adding hard throwers who can reasonably find the strike zone is expensive, and up until very recently, the D-backs' payrolls did not match even the mid-market teams, let alone the big market teams, who often spent big on such relievers.

There's a new game in town for the Diamondbacks, however. Manager Torey Lovullo acknowledged as much during his pre-game press conference on Sunday. "There's a lot of octane coming out of the bullpen now," he said.

Right-hander Justin Martinez leads the pack with an average fastball velocity of 100.6 MPH. That extreme heat, in combination with his devastating splitter at 90 MPH, has made him one of the most dynamic pitchers in the game and drawn national attention.

Co-closer and lefty A.J. Puk is rushing it up there at 96.3 MPH. Ryne Nelson (95.5), Jalen Beeks (94.7), and Shelby Miller (94.5) all have above-average velocity. Even Bryce Jarvis is averaging 93.8.

Lovullo pointed out that the team still has a couple of pitchers with low arm angles that can cause trouble for hitters, despite lower velocity, such as Ryan Thompson (90.3) and Joe Mantiply (88).

"I like that diversity, and a different type of delivery," Lovullo said. "So we have octane and then different looks. I think we try to do that by intent. But there's no replacement for velocity. When you can throw the ball at that speed and know where it's going, it's a true gift, and we have that in the bullpen."

Roster Crunch

The D-backs have more velocity on the way, too, coming from the injured list and Triple-A Reno. Kevin Ginkel, whose fastball typically averages around 96 MPH, is working his way back from right-shoulder inflammation. He'll likely be back by the end of April, if not sooner.

Kendall Graveman averaged 96 MPH from 2021-2023 as well, but missed all of last year due to shoulder surgery. He's been out with a lower back strain and is a little behind Ginkel. It remains to be seen just how hard he is able to throw when he finally makes it back, or if he stays healthy. But if he can, he's another power arm to add.

And then there's Drey Jameson. The 27-year-old righty is coming off Tommy John surgery and averaging 98.8 MPH on his four-seamer, and just shy of 95 MPH with the two-seamer for the Reno Aces. He's struck out 10 batters in 5.2 innings and has yet to issue a walk.

Per Lovullo, Jameson still has a couple of boxes to check, such as pitching on back-to-back days, going more than one inning, and seeing how he recovers from that. But he's close too, and should achieve those milestones before the end of April.

How the D-backs work out the looming bullpen roster crunch is anybody's guess. Lovullo left no ambiguity about Ginkel and Graveman's spots on the roster when they're ready to come off the injured list.

"When they're healthy, they're coming back, they have spots on this team, that's for sure," said Lovullo. "Where that takes us, I don't know yet. It gives me a little bit of anxiety to have to figure that out, but I'm not going to worry about it till I have to. It's imminent, we know they're coming, we know we have tough decisions to make, and we're going to get better when they join us."

Solutions and Options

The options the team has are several-fold. Bryce Jarvis and Joe Mantiply both still have minor league options. Jarvis has pitched well, striking out seven batters, walking just two, and allowing two runs in 5.2 innings thus far. But he could well be a victim of this roster crunch.

Mantiply, who is a 34-year-old veteran and former All-Star, still has two minor league options, oddly enough. He has struggled mightily with declining velocity and high hit rates of late. He has a 12.71 ERA in 5.2 innings, albeit with a 4.59 FIP and a 2.01 Statcast xERA.

Then you have Ryne Nelson, who has been working out of the bullpen, and barely keeping his pitch counts up high enough to be considered "stretched out. His last three outings have been in the 31-36 pitches range. He could very well be optioned down to Reno to stretch back out to a true starter's workload.

As good as the bullpen has been, it could look somewhat different by the end of April. Stay tuned to Arizona Diamondbacks On SI as we continue to bring you the best and most comprehensive D-backs coverage in the market.

See also the Snake Territory Podcast with Jesse Friedman and myself. We discussed the bullpen at the 24 minute and 42 second time stamps