Zac Gallen Continues to Chase History

The Arizona Diamondbacks don’t generate a lot of national headlines these days, but the team’s ace, Zac Gallen, is trying his best to change that. Since a Luke Maile double knocked him out of a game against the Guardians on August 2, Gallen has racked up six consecutive scoreless games, covering 41 1/3 innings. Gallen’s run has gone on long enough to have historical significance: He currently ranks 17th in baseball history, at least the history during which usable game logs exist (since around the start of the 20th century). He’s two outs from catching Brandon Webb’s 2007 streak to set a new Diamondbacks franchise record, and another 3 2/3 innings will slot him into the top 10, tying his with the streaks of Cy Young, Sal Maglie, and Doc White.

Naturally, most streaks of this nature involve a player playing well above their established level of ability, and Gallen is no exception. But every pitcher with a scoreless innings streak this long was at least solid, with nary an incompetent journeyman in sight. Gallen is again no exception and was having a solid season even before the streak started. Entering play on August 2, he had an ERA of 3.24 and a FIP of 3.69 in 19 starts, above-average numbers, though not good enough to force his way into the Cy Young conversation. (Earlier today, Baseball Prospectus‘ Michael Ajeto published a deeper examination of some of the changes Gallen has made during the scoreless streak that is worth a read.)

Gallen has enjoyed some good fortune during this run, but he’s also better established his bonafides as a no. 1 starter in the last month. His 1.47 FIP is third in baseball over that stretch, behind Spencer Strider and George Kirby, and despite not being known as a dominating strikeout pitcher, he’s sixth in baseball in strikeout rate. That success also carries over into Statcast’s xStats:

Strider and Jacob deGrom intrude if you reduce the qualification to 400 pitches, but however you carve things up, Gallen has been pitching at an elite level.

Naturally, a run like this will have an effect on the long-term projections:

ZiPS has been high on Gallen since his successful promotion to Triple-A New Orleans in 2018, seeing him as a very polished pitcher for his age. But a stress fracture to his arm last year derailed him early, and he never got back to the level of his first two seasons in the majors, finishing 2021 with career-worsts in FIP (4.25), hard-hit percentage (42.4%), and a panoply of plate discipline stats. Gallen’s 2022 puts him back on his pre-2021 trajectory:

Arizona has Gallen for three more cost-controlled seasons, but the clock is ticking if they want to get an extension done at any sort of a discount. It’s all arbitration seasons from here on out, so any leverage the team has to make a good deal will start to evaporate very quickly, and Gallen’s agent, Scott Boras, is not known for giving out contracts that are overly team friendly. ZiPS suggests a six-year, $102.6 million extension, covering three free agent years, as a fair offer.

With Gallen dominating, the Diamondbacks have played solid baseball, going 17-10 since he started his streak, leaving the Snakes within striking distance of the .500 mark. They’ve even snuck up on the floundering Giants. They’re now are only a half-game behind, quite the sea change from the 55 games they finished behind San Francisco in 2021. At eight games back in the Wild Card race, postseason baseball is a long shot, but there’s at least a whiff of plausibility.

Now, what are the chances that Gallen gets the 18 innings required to beat Orel Hershiser’s record of 59 scoreless innings? Based on the run environment and Gallen’s current projections, ZiPS thinks there’s a 23% chance of a team scoring at least one run against him in any given inning. Now, you could go all binomial distribution on that and say that there’s a 0.9% chance of catching Hershiser, but you’d actually be underrating Gallen’s likelihood. There are more hit streaks, scoreless streaks, and home run streaks than you’d expect if you assume that level of certainty about a player’s ability. Looking at what the rate of these streaks implies, you see ability as something that ebbs and flows over time. Not knowing what Gallen’s “true” run prevention ability is, ZiPS projects that he actually has a significantly better shot (2.2%) of getting to 59 1/3 scoreless innings. He can thank 2022’s run environment for part of those good odds; the change in likelihood doesn’t move in a linear fashion with league offense, and going back to 2020’s environment drops that probability to just under 1%.

That being said, records tend to be set in environments that make it easier to break them, so there’s no shame in getting a boost from baseball’s lack of offense. Hershiser notched his record run in a very low-offense environment, and many of the longest streaks were set in the Dead-ball Era. A 1-in-50 chance at breaking a significant record is always exciting, and Zac Gallen may have already done something even more difficult: he’s made September Diamondbacks games must-see TV.