How Should the Brewers Align the Starting Rotation in 2024?

Only one team every five years or so makes it through an entire season with five starting pitchers. Even those teams will give one or two spot starts to an extra guy, but there is a team about twice each decade who only needs their top five to do any very important work. Still, that's rare enough to ensure that no team really plans its season around five starters. You need six. In fact, you need 10.

Happily, the Brewers just might have 10, at least at this moment. Even after losing Brandon Woodruff to the vagaries of pitching and trading Adrian Houser to clear some salary from their prospective payroll, they have the following hurlers slotted into their projected rotation for 2024:

• Corbin Burnes
• Freddy Peralta
• Wade Miley
• Colin Rea
• Joe Ross

Behind that group is a much less reliable group, of course, but also an unusually talented and interesting one. Certainly, this constitutes the best "second line" of any rotation in the NL Central:

• Robert Gasser
• Aaron Ashby
• Janson Junk
• Carlos F. Rodríguez
• Jacob Misiorowski

It's unlikely that Misiorowski will be ready for the big leagues as a starter in 2024, but even without him, that's a nice depth corps--almost enough so to make one overlook the relatively unimpressive back end of the group above it. After all, if Rea or Ross needs to be replaced midstream in order to give the team a legitimate chance to reach the postseason, Gasser and Ashby are awfully encouraging options. Nor does the above account for the availability of 2023 long relief ace Bryse Wilson to move back to the rotation, if a dire need arises.

In fact, Gasser and Ashby, especially, are good enough to make it worth entertaining the notion of a six-man rotation for a moment. That wouldn't be totally novel in Milwaukee, after all, and there are multiple reasons why the 2024 team could be as good a fit for it as the 2021 club was. That year, using six starters and lengthening the time between starts for everyone was a response to the shortened pandemic season of 2020. This time around, it would be more about roster construction, but health would be part of the calculation, too.

Miley, Rea, and Ross have such extensive injury histories--and Miley, who turned 37 last month, is showing the signs of his age so clearly--that lengthening their recovery timeline between each outing makes ample sense. Rea is a good example, too, of how the extra rest can make a difference in sheer performance. He allowed a .778 OPS when starting on four days' rest last year; a .767 when starting on five days; and a .596 when working on six or more days of rest. The samples there are too small to draw too much from them, but note, too, that Rea's average velocity on each of his two fastballs was about half a tick higher when starting on five days than on four.

Of course, those guys aren't the reason why you don't use a six-man staff, anyway. It's not a great revelation to say that back-end starters might benefit from extra rest, especially because Gasser and Ashby are (by consensus) not much worse than Rea and Ross, if they're worse at all. It's the front end of the rotation, with prime-aged Burnes and Peralta, that makes this idea tough to embrace, so let's turn our attention there.

Firstly, if we're going to talk about these two, we have to acknowledge that it might well be just Peralta in the mix, come Opening Day. It's impossible to predict whether the Brewers will trade Burnes, at this stage, but they certainly haven't ruled that out, and if he were gone, the whole picture would change. In most formulations of a deal, I would expect the team to get back a starter who could be inserted into the rotation some time in 2024, but that pitcher would be very unlikely to be anywhere near as good as Burnes. If they didn't get a rotation piece back, I think the team would go sign another free-agent starter, but again, we're talking something closer to Miley than to Burnes at that point.

In any scenario in which the team trades Burnes, then, they're likely to have the same number of credible starters, but one fewer hurler who stands out from the rest of the mélange. That would only make a six-man staff more viable. Let's consider the situation as-is, though. I think a strong case can be made for using the longer rotation even with both Burnes and Peralta in place.

Both of those pitchers enjoyed their best seasons in 2021. Moreover, they've quietly been used mostly on six-day rotations even in the seasons since. Of his 97 career starts, Peralta has made only 22 on four or fewer days. He's been best (.618 opponent OPS) on five days, and better (.651) on six or more than on four (.678). Burnes has made just 31 of his 106 career starts on four days. He's been slightly better (.583 opponent OPS) on regular rest than on longer rest (.599), but the difference is pretty small. 

Moving to a six-man rotation would increase the likelihood of both aces staying healthy throughout 2024, so it's unlikely the team would face much pushback from either. This is the last guaranteed year of Peralta's very team-friendly contract extension, and Burnes is due to hit free agency after the campaign, so each has plenty to gain by minimizing injury risk. The only real question is whether trading anywhere from five to 10 starts by those two for the same number by Gasser or Ashby would hurt more than it would help.

To be sure, there's a wide gap between the expected performances of the Crew's top two starters and their sixth and seventh guys. Baseball Prospectus has already published the early version of their PECOTA projections for 2024; here are the key numbers for the four pitchers in question. (DRA- is the rate version of their Deserved Run Average. It's scaled to 100, where that number is average and lower is better.)

It would have been rather shocking to find that there would be no performance tradeoff in lengthening the rotation. We have no such shock from which to recover. The likes of Gasser and Ashby are not going to neatly mimic Burnes and Peralta every time through. If they were expected to do so, they'd already be written into the rotation. Note, though, that the system only pegs Burnes and Peralta for 29 starts apiece, anyway. Coincidentally (or not), BP's depth charts also project Gasser and Ashby to combined for 29 starts. 

Some of that is just the natural conservatism of projection systems, but not all of it can be explained that way. To take one example, Burnesian workhorse Gerrit Cole is projected for 31 starts. The system is nodding toward both the risk of injury and the team's recent tendency to lengthen the rotation whenever it can. Given that, maybe it makes sense to accept a fistful of starts from the two lesser (but certainly adequate) starters above, rather than trying to change recent patterns of usage for Burnes and Peralta to make up for the absence of Woodruff.

Add to all of this the fact that, as the game evolves, more and more starts are made on what is still nominally considered "extra" rest, anyway. More starts were made on at least five days of rest in 2023, league-wide, than ever before. In the minors, the new schedule (six-game series each week, with a regular Monday travel day) has led to most starts being made on five or six days of rest. As pitchers from Japan's NPB (where starters pitch once a week) filter into MLB in greater numbers, teams are trying to accommodate them to various degrees. It's possible that using a five-man rotation, in 2024, constitutes clinging to an essentially extinct concept.

On balance, it makes a lot of sense for the Brewers to think of themselves as building a six-man rotation for 2024, if they want to defend their NL Central title. We'll see to what extent the team agrees, over the first six weeks of the new year.

What's your stance on the question of five starters or six? How would you line up the rotation for the coming season? Let's discuss it in the comments.