by Matt Wilkes

Should the Reds explore a six-man starting rotation?

Baseball will look categorically different this year. From the shortened schedule to expanded rosters, taxi squads, and various rule changes, many aspects of the game will be unlike anything we’ve seen before. It will undoubtedly lead coaches to manage their rosters in creative ways. One such possibility is implementing six-man rotations.

Two teams — the Angels and Mariners — have already announced they will use six-man rotations.

The Reds have already announced they will use a five-man rotation consisting of Sonny Gray, Luis Castillo, Trevor Bauer, Wade Miley, and Anthony DeSclafani. Tyler Mahle and Lucas Sims will be used as “piggyback” starters (essentially long relievers) to pick up the slack from rotation members who don’t go deep into games.

But would a six-man rotation make more sense? It’s a strategy often discussed but seldom deployed. Is it used infrequently because teams are stuck in tradition, or because it’s ineffective? Let’s dive in.

Why would a team use a six-man rotation?

With abbreviated training camps, teams are understandably worried about injuries. Players have had limited time to ramp up before Opening Day — especially compared to the normal length of spring training — prompting the fear for soft-tissue injuries for all players and arm troubles for pitchers. Many pitchers will not be stretched out to the point where they can throw 100 pitches in a game to start the season. Teams are almost certainly going to use the bullpen early and often.

As an extra precautionary step to preserve pitcher health, a team could implement a six-man rotation to give its starting pitchers five days of rest between starts instead of four. In theory, the extra day of rest would also improve pitcher performance because they would stay fresh. The Angels are hoping this approach works to protect star pitcher Shohei Ohtani.

Another argument for a six-man staff: a team has so many good options that it doesn’t want to leave one out of the rotation. A team with good depth could conceivably give all their pitchers more rest without a huge drop-off in performance at the back of the rotation. Rebuilding teams, like the Mariners, may roll out a six-man rotation to give prospects more opportunities while limiting their innings.

Would it actually work for the Reds?

The Reds certainly have the depth to pull it off. Behind the starting rotation, the team has Mahle, Sims, Jose De Leon, Tejay Antone, and Tony Santillan at its disposal. The first three have various levels of big-league experience and success. As things currently stand, Mahle would likely be the sixth starter.

One couldn’t blame the team for wanting to be cautious with a starting rotation that was recently named the third-best in baseball. If the Reds can get to the postseason, they’ll have a huge advantage in getting to unleash arguably the best trio in the National League. But Castillo, Gray, and Bauer need to stay healthy for the Reds to maintain that edge. An extra day off between starts could prove beneficial.

There are obvious downsides to a six-man rotation, however. The biggest is, of course, taking away starts from the team’s best pitchers. In a 60-game season, each pitcher in a five-man rotation should get 12 starts, assuming good health and performance (large assumptions, to be sure). Pitchers in a six-man rotation would only get 10 starts apiece, which would take six combined starts away from Castillo, Gray, and Bauer. Those six games could be the difference between making and missing the playoffs in a shortened season. In 2019, four teams missed the playoffs by fewer than six games — and that was in a 162-game season.

How much would those lost starts hurt the Reds? In theory, the sixth starter would need to at least match the value lost by taking away starts from the best pitchers. They would at least have the advantage of getting 10 starts to match the value provided by the top three members of the rotation. That doesn’t seem inconceivable on first blush — would it really happen, though?

To give us an idea, let’s look at the Steamer and ZiPS projections for the 2020 season. Specifically, we’ll look at Wins Above Replacement and adjust it for both 10 starts and 12 starts for each pitcher. Steamer projections have already been adjusted for the shortened season but do not project Mahle as a starter. It also does not project Gray for 12 starts. To adjust for this, I look at projected WAR per inning pitched and extrapolate based on each starter’s projected average start length. For Mahle, we’ll assume the average start is five innings. Here’s where we end up:

Per this projection, the Reds would lose a combined 0.7 WAR by taking away six total starts from Castillo, Gray, and Bauer. They would gain just 0.4 WAR from giving 10 starts to Mahle. The team would also lose an additional 0.2 WAR by taking away two starts each from DeSclafani and Miley, bringing the total lost WAR to 0.5. Not a great trade-off. In a 162-game season, losing 0.5 WAR is not ideal — but its effects aren’t felt as much. In a 60-game season, that could be highly detrimental. Per the Steamer projections, 0.5 WAR is equivalent to the value Castillo alone brings in five starts.

The Steamer projections are a bit conservative and bearish on the Reds’ staff, so let’s look at ZiPS as well.

ZiPS is a bit more optimistic about the Reds’ staff. In this situation, Mahle would just barely make up for the WAR lost by taking six starts away from the top three members of the rotation. ZiPS actually projects Mahle to perform better than DeSclafani and Miley this season, but taking additional starts away from them tips the scales against the six-man rotation. The Reds would lose 1.0 WAR while gaining only 0.7 back from Mahle.

This is a fairly simplistic way to view the effects of a six-man rotation, but it’s clear that — in a vacuum — taking starts from better pitchers and giving them to a No. 6 starter hurts the team (and for what it’s worth, the results would be similar if we inserted Sims into the hypothetical six-man rotation).

If the team made the playoffs anyway and Castillo, Gray, and Bauer were fresher in October, that would be great. But it’s a risky bet to make. Is there evidence that extra rest improves pitcher performance?

The data shows no noticeable effect, according to research performed by sabermetrician Russell Carleton. Pitchers largely perform the same after five days of rest as they do on four days of rest.

Research by Rob Arthur did find, however, that a six-man rotation has some effect on preventing injuries, at least in the short term.

“I found that there is a strong link between rest and injury rates. Looking at starts on three days of rest, 1.7 percent of pitchers suffered a reported injury within the next two weeks. At four days of rest, the typical amount in the modern age, that number drops precipitously to 1.0 percent. (Maybe that helps explain why the five-man rotation came to be.) Then the injury risk falls even further: at five days of rest — which would be standard for a six-man rotation — just 0.8 percent of pitchers are injured in the next 14 days, for a 20 percent decrease compared with four days of rest. That is a potentially meaningful drop in injury risk.”

It’s unclear whether this strategy would have long-term effects on preventing injuries. As Arthur puts it: “perhaps more rest merely delays the inevitable.”

Ultimately, a six-man rotation doesn’t make much sense for the Reds despite their pitching depth. And clearly, the coaching staff and front office have reached the same conclusion. While it’s a fun idea to think about, it doesn’t make sense to take away starts from three of the top pitchers in the NL, especially when there’s no certainty about the effect the six-man rotation has on pitcher health.

The team can still use its starting pitching depth advantageously, though. Mahle and Sims will see plenty of innings regardless of whether they’re in the rotation or bullpen. They’ll be needed early in the season as the starters build up the stamina. Additionally, starters will also have shorter leashes in general because every game is vital — as Bauer pointed out, one game in the 2020 season is worth 2.7 games in an ordinary 162-game campaign.

While a larger-than-normal rotation won’t happen, the Reds finally have pitching talent that allows them to get creative and adapt to an unusual season.

Photo Credit: R.J. Oriez

Matt Wilkes got hooked on Reds baseball after attending his first game in Cinergy Field at 6 years old, and he hasn’t looked back. As a kid, he was often found imitating his favorite players — Ken Griffey Jr., Adam Dunn, Sean Casey, and Austin Kearns — in the backyard. When he finally went inside, he was leading the Reds to 162-0 seasons in MVP Baseball 2005 or keeping stats for whatever game was on TV. He started writing about baseball in 2014 and has become fascinated by analytics and all the new data in the game. Matt is also a graduate of The Ohio State University and currently lives in Columbus. Follow him on Twitter at @_MattWilkes.

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6 months ago

Bauer says he’d like to to pitch every 4th day. Some other starters like an occasional 5 days rest but generally prefer 4 days. Just something else to consider, everyone will have to make adjustments this year.