Will the Veterans in the Diamondbacks Rotation Step Up ?

Results were supposed to improve for the D-backs rotation in August, but they haven't, yet

Aug 10, 2024; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen (23) on the mound in the third inning during a game against the Philadelphia Phillies at Chase Field. Mandatory Credit: Allan Henry-USA TODAY Sports / Allan Henry-USA TODAY Sports

The narrative for the Arizona Diamondbacks through the early and middle summer was once the veteran starters returned from the Injured List, the team would have one of the best rotations in the league.

Zac Gallen missed a month from May 31st to June 28 due to a hamstring injury. Merrill Kelly went down with a shoulder strain in mid-April and did not return until August 11th. Eduardo Rodriguez didn't even make it to opening day before landing on the injured list with a shoulder strain of his own. He finally made his season debut on August 7th.

Even Jordan Montgomery, whose season started April 19th without a spring training due to signing late, landed on the injured list too. Montgomery spent 25 days on the injured list due to left knee inflammation from June 29th to July 23rd.

With all those missing starts from the top four projected starters, the results were predictable. Through July 31st the Diamondbacks had a team starter's ERA of 4.68, which ranked 26th in MLB.

That was due in part to Montgomery posting a 6.51 ERA in his first 15 starts. But the starters called up from Reno did not pitch well either. Slade Cecconi had a 5.75 ERA in 13 starts. Tommy Henry posted a 6.47 ERA in seven starts.

Ryne Nelson had a 4.91 through his first 18 starts, although he had already started turning the corner in early July. Cristian Mena was called up but lasted just three innings, allowing four runs, and was sent back down. Yilber Diaz made four starts. The first two were excellent, but the second two went poorly and he was optioned back out.

The rotation was held afloat in large part by Brandon Pfaadt, who became the most reliable starter on the team, going deep into the games on a consistent basis. He led the team in innings through the end of July (and continues to do so) while posting a 3.92 ERA.

D-backs Rotation Since August 1st

Surely once Rodriguez and Kelly came back, the rotation would stabilize, right? Well, not so much. In 17 games in August the starting rotation has a 4.98 ERA , which ranks 21st in MLB. The team has gone 12-5 in those games, thanks to an offense that has scored 6.3 runs a game this month.

The below table shows the individual starters ERA since August 1st. Alongside side that is the FIP. That is Fielding Independent Pitching. It's based on strikeouts, walks, and home runs. It's considered somewhat more predictive of ERA than ERA itself.

D-backs Starters since August 1st / Jack Sommers

The encouraging thing here is that every starter except except Rodriguez has a FIP lower than their ERA. The cumulative FIP is 1.29 runs lower than the ERA. That may portend lower ERA going forward.

Kelly and Rodriguez each have only two starts this month, but have combined for an ERA over 6.00. Perhaps most concernining is Kelly's velocity loss, down 2 MPH in his last start to 89.9 MPH. He said it's not a concern for him unless it stays down that low. That will be watched closely.

Zac Gallen meanwhile has been struggling to record strikeouts and swing and miss, and has been forced deep into counts, leading to shorter outings. Montgomery continues to be up and down with his effectiveness. Some games it looks like he's getting it together, only to be blown up in his next start.

While the Arizona Diamondbacks continue to decide who will remain in the rotation, Ryne Nelson or Jordan Montgomery, it's imperative that Zac Gallen, Merrill Kelly, and Eduardo Rodriguez begin to get better results.