Will the New “Year of the Pitcher” Crown a New ERA Champion?

Jacob deGrom‘s already microscopic ERA needs even a stronger microscope to spy it after his outing Monday, a six-inning shutout against the Arizona Diamondbacks that lowered his ERA to 0.71. We’re no longer in April, and we’re not even in May, so this new level of dominance can’t be easily ignored as the product of a small sample. Once performance of this magnitude reaches June intact — and 0.71 is deGrom’s second-highest seasonal ERA after the end of an outing — you have to seriously give at least a thought to the prospect of a pitcher making a run at Bob Gibson’s live-ball ERA record.

We had a chance at this happening last year, thanks to the asteriskesque 2020 season and its 60-game slate, shortened as a consequence of COVID-19. I talked about the possibility going into last season, with ZiPS projecting a one-in-four shot of someone catching Gibson’s 1.12. Nobody did it in the end, but Shane Bieber’s 1.63 was the one of the best ERAs for a qualifying pitcher since Gibson’s in 1968. Bieber and Trevor Bauer, the two pitchers who came closest, fell well short of Gibson but given the relatively high levels of league offense, their efforts were enough to get them the third and fourth spots on the all-time single-season ERA+ ranks.

Catching Gibson in a 60-game season would have been an accomplishment, but not really a full one. Records are naturally set in conditions that benefit players, and Gibson was no exception: 1968 was dubbed the Year of the Pitcher thanks to a league ERA of 2.98, nearly a half-run lower than any season since the spitball was banned. Gibson’s 258 ERA+, which takes into account league offense, still sits atop the leaderboard, but at least it doesn’t utterly wreck the recent field, which consists of Pedro Martinez (243, 1999), Roger Clemens (227, 1997), and Zack Greinke (227, 2015) among others.

But since 2021 is a full 162-game season, catching a 1.12 ERA would feel a lot less like sneaking in through a loophole. A significant drop-off in league offense (to a 4.02 ERA) could be credited for an assist, but it’s not a number that is unfair relative to baseball history. So, can he do it?

deGrom has missed a few starts so far in 2021, with no apparent ill results to his performance, and the Mets have been cautious with his pitch totals; he’s averaged fewer than 70 pitches in his last three starts. That’s beneficial to his chances, as no star pitcher has a long-term ability to keep their ERA that low, even Gibson; just clearing the one-inning-per-team-game requirement optimizes things. deGrom will likely end up with around 30 games started this season, so a good place to begin in gauging his odds is to see if anyone’s come close to 1.12 in a span of 30 games starts, crossing over seasons, since 1920. I’m only listing unique 30-game runs since there is naturally quite a bit of overlap in runs:

Gibson’s best 30-game span was even better than his 1.12 ERA, dipping under one. J.R. Richard’s presence on this list is especially cruel, as his 30-game span ended with the final game of his major league career. Before Richard’s next start, he suffered a stroke caused by a blood clot, and while he attempted a comeback a few years later in the minors, he was no longer the same pitcher.

Nobody catches 1.12 on this list, but many come close enough that the result is at least plausible. Jake Arrieta was only a run from accomplishing the feat. deGrom himself appears on this list, his 30-game span running from April 21, 2018, through April 3, 2019. His 1.40 ERA over 30 starts comes out to an ERA+ of 266 in a higher run environment (by about a tenth of a run) than 2021 so far. A tenth of a run isn’t a lot, but to break a record like this, every advantage helps. Yes, Mets fans, I see that 10-9 record for deGrom over that stretch.

To get an idea of deGrom’s probability of finishing with an ERA of 1.12 or better, I worked with a technique I’ve used in the past, which “simulates” a season using Monte Carlo algorithms and a smoothed model of a pitcher’s starts based on their projections and historical usage. At 189.2 innings (what he has in the bag, plus the 22 starts of 6.3 innings per start in his depth chart projections), he needs to allow 23 or fewer runs or a 1.23 ERA for the rest of the season. At 162 total innings, he’d have to maintain a 1.30 ERA the rest of the way.

deGrom’s no slam-dunk to catch Gibson, but he’s got a fighting chance, with my model estimating a 3.1% chance to beat a 1.12 ERA, or more precisely, Gibson’s 1.122538 (no cheating with rounding here!). That’s about 31-to-1, a little better than getting the exact number in roulette and roughly the probability of a 20-homer hitter getting a round-tripper in any given at-bat. In other words, it’s more likely than not that he falls short of the feat, but it’s definitely possible and firmly in the realm of plausibility.

Jacob deGrom is having the best run of his career and quickly developing a Hall of Fame case based on Koufax-levels of peak performance. Catching Bob Gibson would be a fantastic sentence on a plaque in Cooperstown. Hopefully, the Mets’ offense has the decency to give him more than 10 wins if it should come to pass!