Young Arms Are Flourishing in the Diamondbacks’ Veteran Rotation

Editor’s Note: This article was written prior to Pfaadt’s poor start against the Mets on August 27, in which he gave up six earned runs in 4.2 IP.

Brandon Pfaadt was a lifesaver for the Diamondbacks last October. The young right-hander put his up-and-down rookie campaign in the rearview mirror and absolutely shoved as Arizona’s No. 3 starter in the postseason.

Over five outings, Pfaadt pitched to a 3.27 ERA. He struck out 26 batters in 22 frames. The D-backs won four of his five starts. He was the breakout star on a breakout team amid a memorable NL pennant run.

Yet, when the 2024 season began, the Diamondbacks were probably thinking they wouldn’t need Pfaadt in the playoff rotation at all.

The D-backs bolstered their rotation over the winter with veterans Eduardo Rodriguez and Jordan Montgomery. With Rodriguez and Montgomery slotting in alongside Zac Gallen and Merrill Kelly, Pfaadt was destined for a bullpen role – if that – on Arizona’s potential postseason roster.

Brandon Pfaadt Has Been the Rock of the D-backs Rotation

Yet, five months into the 2024 season, Pfaadt is the only qualified starter on the Diamondbacks roster. He ranks seventh in the National League with 150.0 innings pitched. He is one of only six qualified NL starters averaging at least six innings per outing.

Pfaadt also leads the D-backs with 2.8 FanGraphs WAR. His 4.08 ERA won’t drop any jaws, but the righty ranks seventh among qualified NL arms with a 3.52 xERA. His 5.1% walk rate ranks fourth.

Moreover, pitch modeling systems are enamored with Pfaadt’s arsenal this year. His 2.84 PitchingBot ERA leads all qualified NL pitchers. His 107 Pitching+ ranks fourth. Both systems agree he has dominant pure stuff and excellent command.

The Diamondbacks are 15-10 in his starts.

Pfaadt’s emergence as a reliable mid-rotation arm has helped the Diamondbacks weather injuries to Rodriguez, Kelly, Gallen, and Montgomery, in addition to Montgomery’s generally disappointing season.

It remains to be seen how manager Torey Lovullo will line up his rotation for a potential postseason series, but Pfaadt is certainly making his case to start in October. And he’s not the only young D-back who has impressed this season.

Ryne Nelson Is Enjoying the Opposite of a Sophomore Slump

Ryne Nelson ranked third on the Diamondbacks with 144.0 innings pitched last season. However, his results were poor, and his underlying numbers equally so.

Out of 59 NL pitchers with at least 100.0 innings pitched, only four had a higher ERA than Nelson’s 5.31. Only seven had a higher FIP, and only nine a higher xERA.

The Diamondbacks had so little faith in Nelson last October that they relied on a three-man rotation, opting for bullpen games when Gallen, Kelly, and Pfaadt were unavailable.

When the team signed Montgomery in March, Nelson was relegated to a depth role.

Yet, aside from Pfaadt, Nelson has thrown more innings than any other D-backs pitcher this year. With a 4.29 ERA and 2.1 fWAR in 24 games (22 starts), he has established himself as a viable rotation option – so much so that when the D-backs finally had all their arms healthy, they chose to move Montgomery, not Nelson, to the bullpen.

The Diamondbacks didn’t believe in Nelson last October. But they believe in him now.

Nelson isn’t quite in the same league as Pfaadt – there’s a reason Pfaadt was the higher-ranked prospect – but his numbers are solid across the board. PitchingBot and Pitching+ will tell you he has outpitched everyone but Pfaadt in the Diamondbacks rotation this year:

Young Arms Have Picked Up the Slack in the D-backs Rotation

Let me be perfectly clear: Neither Brandon Pfaadt, Ryne Nelson, nor anyone else is coming to dethrone Zac Gallen as Arizona’s ace.

Similarly, Merrill Kelly and Eduardo Rodriguez are probably still the No. 2 and 3 starters come October.

All the same, it’s pretty incredible that in a rotation loaded with proven stars, the two most important contributors have arguably been Pfaadt and Nelson.

If the Diamondbacks are going to make some noise in the playoffs, they’ll need their veteran starters to step up. Still, they wouldn’t have made it this far without huge contributions from their sophomore arms.