How baseball’s last major stoppage affected starting rotations

Good morning, all.

The NFL season is now behind us, which for me (and I imagine many others) marks an unofficial date of significance on the baseball calendar. Before too long, the transition from offseason into Spring Training will be complete and we’ll have on-field action to discuss again. Granted, the Super Bowl feels less like a line of demarcation when a fairly substantial portion of MLB offseason transactions have yet to occur. Either way, many of the baseball routines we take comfort in are making their annual rounds. Case in point: the recently-released PECOTA projections left basically everyone except Dodgers fans Mad OnlineTM. The more things change, the more they really do stay the same.

That said, we would be fooling ourselves by peddling the idea that the 2021 season will be normal when compared to anything other than its immediate predecessor. These inevitable uncertainties certainly complicate any sort of predictive analysis. How will the current economy of baseball affect this season? To what extent will we notice the effects of a minor league season that was, for all intents and purposes, wiped out in 2020? Today, I want to focus on a question we do have some precedent for, which is the matter of starting rotations.

It goes without saying that the raw number of innings pitched was significantly down last year due to the shortened 60-game schedule. I was curious to see if history could tell us anything about how such a situation impacts two metrics in the following season: average innings per start and average number of starts per starter. The best point of comparison is likely the 1994-95 strike. Of course, this is far from a perfect parallel to the pandemic. Both the 1994 and 1995 seasons were closer to full-length than not, and strained labor relations don’t impose the same training restrictions as COVID-19. Nevertheless, let’s take a look and see if we can find anything. First, the pertinent stats for 1994:

This appears to be pretty normal. The average start length is slightly lower early on before ramping up a tad as we moved deeper into the summer. Take the August numbers, especially the average starts per pitcher output, with a grain of salt considering the last games were played on the 11th of that month.

But those were numbers largely unaffected by the strike. Now, 1995:

The GS/SP number taking a nosedive in April makes sense; Opening Day wasn’t until April 25th, so most teams only had time to make one trip through the rotation. Related to the delayed start, and presumably the IP/GS dip as well, was the bizarre Spring Training that unfolded as the labor dispute remained unresolved. The “first” Spring Training consisted of potential replacement players before the strike ended in early April, giving enough time for a brief “second” Spring Training. By June, however, the average start length was equal (6.13 innings) to what it was during that month the previous year.

If we go a year further, here’s 1996:

Back up to 162 games, the only major difference here is that the “April effect” on innings-per-start isn’t as pronounced as it was in 1995. Start length had stabilized by May and held steady until the usual dip in September.

Let’s contrast all of that with what we saw in 2020, including 2019 as a baseline given the changing trends in starting pitcher usage over the past couple decades.

IP/GS unsurprisingly opened low last July, but never recovered to 2019 levels as was the case following the strike. This is understandable given the influx of doubleheaders, workout restrictions, etc. that cropped up last year, which also pushed the GS/SP figures down. What that means for 2021 is anyone’s guess. The overall taxation on pitchers’ arms was lighter in 2020, but that’s largely because of the aforementioned challenges in preparing that also contributed to a spike in injuries. Pair all of that with the baseball meta increasingly shifting away from conventional pitching management, and the odds of 2021 metrics bouncing back to their 2019 rates seem slim-to-none. Baseball is an evolving game; the pandemic may have simply accelerated the changes that were already in motion.