In May, the Diamondbacks had 17 quality starts. Quality starts often require the bullpen to pitch less innings. Those starts should keep them rested. More importantly, the interesting question is whether the Diamondbacks relievers pitch better in games in which the starter executed a quality start? Let’s look at that question. Data from Baseball Reference, FanGraphs, and Baseball Savant.

The 17 Quality Starts in May.

There were seven relief pitchers with at least 14 PAs in those quality starts (Pfaadt was not considered because of too few PAs in quality starts).

Zero Earned Runs. Three relievers (Jonathan Loaisiga, Brandyn Garcia, and Taylor Clarke) allowed zero earned runs. That could imply that they were not challenged by their batters. To test that idea, I looked at stats (OBP, SLG, and RBIs/PA) for the batters they faced. I found seven dangerous batters: Luis Arraez, Jake Burger, Oneil Cruz, former Diamondback Jake McCarthy, Bryan Reynolds, Casey Schmitt, and Juan Soto. To my surprise, they each had exactly four PAs against those dangerous batters. My conclusion is they were indeed challenged and pitched admirably. The following table shows the dangerous batters they faced.

Side Note: In 2022, Jake McCarthy was voted Rookie of the Year by the AZ Snake Pit. After last season’s career low .591 OPS, the Diamondbacks traded him during the offseason. This season with the Rockies, Jake McCarthy had a career best .784 OPS and a career best .149 RBIs/PA. Those career best statistics made him a dangerous batter.

Win Probability Added (WPA). In May, which of the seven pitchers made the most impact as measured by WPA? To my surprise, despite allowing earned runs, Kevin Ginkel and Paul Sewald ranked third and fourth ahead of Loaisiga. Another note is that two games (13 and 21 May) were responsible for Juan Morillo ranking last in WPA. The following table shows their WPAs.

Quality Starts in the Entire Season.

Now, let’s look at the big question, “This season, did the Diamondbacks relievers pitch better in quality starts?” Each of their game-WPAs were placed into one of two bins: games with quality starts and games without quality starts. Each reliever had between 7 and 9 quality start games, with the exception of Thompson, who had 5. Sample size was not an issue.

The following table shows the WPA for each reliever.

The answer is that it depends on which relief pitcher.

In May, three relievers allowed zero earned runs in their quality starts, despite facing dangerous batters. They were Jonathan Loaisiga, Brandyn Garcia, and Taylor Clarke. This season, some relievers pitched better in games with quality starts (Loaisiga, Garcia, and Clarke), and some relievers (Morillo, Sewald, and Thompson) pitched better in games with non-quality starts. One reliever (Ginkel) pitched about the same in each type of game.