As of Apr. 14, the Diamondbacks bullpen ranks ninth in ERA (3.29), first in WHIP (.84), first in walks (9) and 11th in strikeouts (59). The bullpen has done considerably well despite injuries to key relievers Kevin Ginkel and free agent acquisition Kendall Graveman. On top of this, the Diamondbacks have a blossoming bullpen arm in Drey Jameson, who’s starting the year in Triple-A. With this in mind, who in the bullpen is finding success on the young season?

The first on the list is Ryan Thompson. The six-foot-five submarine pitcher has been on the Diamondbacks roster since 2023 when the team picked him up off waivers. Since then, Thompson has been a consistent bullpen arm with the team. In 2024, Thompson had a 3.26 ERA in 67 games with the team. This year, he has a 3.38 ERA in his five games, and while the sample size is smaller, he is giving up fewer baserunners per inning. A very effective pitcher for the middle stages of games after building off his struggles in Tampa Bay. 

The next arm in the bullpen is Jalen Beeks. Some fans did not know who Beeks was when he signed, but he has had a powerful start to the 2025 season. Beeks starts the year as a long reliever, a guy who can come in and give the team appearances that span more than one inning (10 innings pitched thus far), but Beeks has been very effective in preventing runs in those appearances. He has a 0.87 ERA and a 0.58 WHIP in seven appearances. This comes after a year when Beeks' ERA was 4.50 in 71 appearances with the Colorado Rockies and Pittsburgh Pirates.

Looking at his advanced metrics, Beeks’ chase percentage is in the 97th percentile of pitchers, the same as his hard-hit percentage and all while generating plenty of ground balls. Beeks has three pitches, but he uses his changeup the most at 43.4% and has yet to give up a hit on that pitch. Beeks provides a second stable left-handed bullpen arm for a team that needs it in a division facing left-handed powerhouses like Shohei Ohtani and Freddie Freeman.

The next guy on the list is another left-handed arm in A.J. Puk. Puk was acquired at the trade deadline for prospects Deyvison De Los Santos and Andrew Pintar. Puk was stellar in his first half-season with the club, producing an ERA of 1.32 in 30 games while tallying 43 strikeouts. Puk has started the year as both a setup man in the eighth inning and a closer. Puk is one of the Diamondbacks' high-leverage arms that has come through for the team. Puk is a perfect 3-3 in save opportunities and has given up two runs in six games with ten strikeouts across those appearances.

Puk excels at forcing batters to whiff on his electric stuff, evidenced by his strikeout percentage (38.5%) and whiff percentage of (37.7%), both in the 90th percentile. Puk will continue to be a guy who will be needed in close games for the Diamondbacks, along with being a left-handed arm for the bullpen.

Another impressive guy is Shelby Miller. Miller was originally a starting pitcher for the club after being traded to the Diamondbacks for a package that included shortstop Dansby Swanson. While Miller struggled as a starter in his few years, he has seemed to make a big turnaround as a reliever upon his return to the team this year. The righty hasn’t given up a run to start his 2025 campaign in five appearances and has only allowed one runner to reach base. The former first-round pick had a very good 2023 with the Dodgers after he was converted into a reliever a few seasons prior, maintaining an ERA of 1.71 in 36 appearances.

Last on the list is young reliever Justin Martinez, whom the Diamondbacks extended right before the start of the season. Martinez had shown flashes of brilliance in 2022 and 2023. His fastball sits in the triple digits and he possesses a devastating splitter that has made him unhittable. While he had a solid ERA of 2.47 in 2024, he walked 36 batters in 72 innings pitched, inflating his WHIP to 1.31. Martinez is young, only 23 years old, and control was something the team wanted to see improve. So far, to start the year, Martinez has delivered.

In his six games, Martinez has not given up a run or a walk this year. He has also converted his save opportunities to give the Diamondbacks key wins. His average fastball velocity sits at 100.9 mph, and he usually sits at 90 mph on his splitter that has some insane movement. 

The Diamondbacks have high hopes for the 2025 season so long as  their hitting and starting pitching continues to perform. Nevertheless, the bullpen has been the key to the team's success through the first 16 games.