How Concerning Are Diamondbacks Rotation Struggles?
The Diamondbacks starting rotation has been a concern this season. Zac Gallen has been terrific, and Merrill Kelly is rounding into form. But Madison Bumgarner was so bad that they had to release him after just four starts, eating over $35 million of his contract. Zach Davies, signed to a one year contract this off season, has made just two starts due to an injured oblique, and is at least two weeks or more away from returning to the rotation.
Ryne Nelson won the fifth starter's role at the end of spring training, and after three decent starts, has been hit hard in each of his last three outings, seeing his ERA sky rocket in the process. Drey Jameson was optioned to Triple-A Reno after two poor starts. Tommy Henry was called up to replace Bumgarner and has only narrowly averted disaster.
Gallen & Kelly vs. the Rest
The gap in ERA between the top two spots in the rotation and the rest of the starters is quite stark. Gallen and Kelly have combined for a 2.57 ERA and 2.93 FIP in 12 starts. The rest of the rotation has a 7.05 ERA and 6.06 FIP in 17 starts. While that's inflated by Bumgarner's astronomically bad performance, none of the other four starters in the second group have an ERA or FIP under five. In total the team starting pitcher ERA of 4.89 currently ranks 20th in MLB and the FIP ranks only slightly better at 17th.
Jack Sommers
Expectations and Projections
In trying to determine what the level of concern should be, the first question one must ask is what were the pre season expectations. The Diamondbacks are 16-13, tied for first place with the Dodgers and a game ahead of the Padres in the NL West. That start may have raised expectations for many that the team should contend for the division title or a playoff spot all season. But is that realistic?
Pre season win projections on most sites that provide such information ranged between 75-78 wins, as did the betting odds for team win totals in Las Vegas sports books. Fangraphs for example only gave the Diamondbacks a 15% chance of making the postseason in their pre season projections, and those odds are still only at 24% despite their current record and position in the standings.
That was due in large part because the pitching staff as a whole was not projected to be very good. Looking at the pre season ERA Projections for the seven starting pitchers (see table below), we can see that Gallen and Kelly have been considerably better than projections, while everyone else has been considerably worse. It's reasonable to expect that Gallen and Kelly's ERA will rise. Whether or not regression in the other direction will take place for the other pitchers remains to be seen. Opportunity may dry up for some of them. (As mentioned, Jameson was already optioned and Bumgarner is no longer on the team)
Jack Sommers
The elephant in the room in the above table is Brandon Pfaadt. Despite having a superior track record in the minors last year, and a better spring training than all of the young pitchers on these lists, he has yet to make his major league debut. We asked the question 10 days ago why he isn't already in the rotation. That could possibly come as early as this Wednesday in Texas, although the team has yet to confirm that. Pfaadt had the second best ERA projection behind only Gallen. Whenever he makes his debut, he will have a lot of high expectations and pressure to help solidify the rotation.
Young Pitcher Development Timelines
While the team is certainly trying to compete in 2023 and has the goal of being in contention for a playoff spot, a certain measure of reality when it comes to young starting pitchers is required. For example just looking over the last five or six seasons, here is a list of pitchers that struggled in their first couple of seasons, but later had varying degrees of success, becoming at least league average starters, or even better:
Logan Webb, Mitch Keller, Josiah Grey, Nick Pivetta, Joe Musgrove, & Pablo Lopez. None of these pitchers had an ERA under 4.00 in their first season, and only two had an ERA under 5.00 (Musgrove and Lopez). As a group, they totaled a 5.40 ERA in their first season in the league. Since then they've been much improved.
*Joe Musgrove has struggled after injury in 2023, and had his 2023 number inflated by a trip to Mexico city. Nick Pivetta has been around or slightly before average innings eater.
Whether or not the D-backs get these types of turnarounds from their young pitching prospects remains to be seen. "Survivor Bias" whereby the team may limit future opportunity for young pitchers to develop in the majors could be a factor as they continue to try to contend. Often times it's the teams that have little hope of contending for the playoffs that can afford to be the most patient, allowing young starters to figure it out in the major leagues.
Summary
If one takes the view the Diamondbacks have a legitimate chance at a playoff spot in 2023 then some concern over the current state of the rotation is warranted. The teams actions indicate they have at least some concern, because they just picked up left-hand starter Konnor Pilkington, as reported by Michael McDermott earlier today.
They'll need a big turnaround from several young pitchers and a bounce back to good health and results from Davies. They also can't afford too much regression for Gallen and Kelly. All of that may be a bit too much to hope for. On the other hand if the view is that the true contention window for this team is probably not until 2024, then allowing the young starters to take their lumps and work through it, while painful at times to watch, is wholly necessary.
