Six-Man Rotations: Who's Doing It and Why It Matters

With only 60 games making up the 2020 regular season, it appears likely some unconventional pitching strategies will be featured.

One strategy that is likely to be somewhat popular is the six-man rotation. So far, two teams have already committed to using six starters for at least the beginning of the season. Others could follow suit, but for now, we will examine the impact it could have for fantasy baseball purposes.

When you're done here, check out our other preseason analysis on starting pitchers including Underpriced Pitchers According to ATC Projections.

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Who's doing it?

Here’s a list of the teams who have publicly discussed the usage of a six-man rotation and decided on whether or not it will be used:

Unfortunately for most starters on those teams, there’s little evidence that extra rest will have significant performance benefits. Starting pitchers weren’t significantly better with extra rest last season, an observation that is in line with research on the subject.

The primary effect of a six-man rotation will be diminished workloads, costing each pitcher two starts in a 60-game season -- the equivalent of five starts in a 162-game season.

However, extra rest can benefit some players and may help curb injury risk.

Who is affected by six-man rotations?

The Mariners are projected to go with a rotation of Marco Gonzales, Yusei Kikuchi, Justus Sheffield, Kendall Graveman, Taijuan Walker, and Justin Dunn. Although there is some room for variation, the Mariners don't have great rotation depth, making their six-man rotation unlikely to change over the season.

In contrast, the Angels' rotation is rife with uncertainty. Andrew Heaney, Dylan Bundy, and Shohei Ohtani are effectively locked into the rotation, as is Julio Teheran if he's ready for the start of the season. The last two spots appear to be up for grabs though, with Griffin Canning, Jaime Barria, Patrick Sandoval, Matt Andriese, Felix Pena, and Jose Suarez all in the mix.

In addition to the Angels and Mariners, the Tigers and Orioles are clubs that could also use six-man rotations this year.

With three top 50 pitching prospects on their 60-man roster, and a core of starters in Matthew Boyd, Spencer Turnbull, and Michael Fulmer, the Tigers may elect to stretch their rotation to six starters for development reasons.

Although the Orioles have less exciting options, manager Brandon Hyde is considering using six starters. If the O's opt for a six-man rotation, then it's likely to be comprised of John Means, Alex Cobb, Asher Wojciechowski, Wade LeBlanc, Tommy Milone, and Kohl Stewart.

How much do decreased workloads change player values?

Losing two starts in a 60-game season can do significant damage to a pitcher's value, but the damage is largely confined to upper-tier, high-workload pitchers. According to Nick Mariano's Expected Draft Value research, innings pitched becomes less important to a pitcher's value the later the pitcher is drafted. In particular, pitcher values become significantly less dependent on innings pitched after pick 50 in drafts.

Since the teams who may potentially use six-man rotations have no starting pitchers being drafted anywhere near the 50th pick in drafts -- Boyd is closest with a 159 ADP -- 10-to-15-inning differences in innings pitched are unlikely to have significant effects on pitcher values. (Ohtani will also hold offensive value, as the Angels intend on using him as a two-way player, which may limit him in some leagues.)

It's important to note that if a player's per-game production doesn't improve with a decrease in innings then their value would decline, but the negative effects of a six-man rotation should be minimal for most pitchers even with that in mind. Still, if a team like the Yankees were to use a six-man rotation, the value of Gerrit Cole or James Paxton would likely suffer.

The Yankees have already decided against using a six-man rotation, but it's useful to see how Cole's value would change in that scenario, in case similarly elite pitchers wind up becoming a part of six-man rotations this year.

Cole is projected for 72 innings pitched this season but if he were to lose two starts then he'd likely end up with closer to 60. A starting pitcher with 63 innings pitched and a 3.00 ERA would have an EDV between 55 and 60. Cole is likely to beat most of the rate stats valued in EDV, but even a more realistic 40 EDV is a far cry from Cole's "normal" value, which has him as an easy top-20 pick.

Pitchers likely to benefit from a six-man rotation

Despite a less-than-stellar rookie season, Kikuchi appears set to benefit from a six-man rotation this season. In addition to working on his mechanics this offseason, Kikuchi cited both the long MLB season and pitching on relatively short rest as contributing to last year's struggles.

Given that Kikuchi was used to pitching on longer rest in Japan, it makes sense that less rest would require an adjustment. A return to longer rest between starts, a shorter season, and revamped mechanics could spur a breakout year for Kikuchi. His 5.46 ERA from last season leaves a lot of room for improvement, but Kikuchi's 418 ADP allows fantasy owners to take a wait-and-see approach on the 29-year-old.

Ohtani, a fellow former NPB pitcher, should also benefit from a six-man rotation. Ohtani hasn’t pitched with fewer than six days of rest since joining the Angels in 2018, and maintaining that amount of rest should help him maintain his performance while mitigating his injury risk.

Given that Ohtani probably wouldn’t have pitched every fifth day in a normal season anyway, the six-man rotation should improve his value as it keeps him on a regular schedule without overworking his arm.

Bundy may also benefit from fewer starts, but manager Joe Maddon's quick hook may be more valuable for Bundy than extra rest. He should be able to throw his fastball less frequently since he’ll face hitters fewer times, which should be good news for his production.

Bundy’s fastball is by far the pitch in his arsenal that has caused him the most issues, and its .378 xwOBA from last season made it one of the hardest-hit pitches in baseball. But Bundy’s slider is elite, and the pitch posted a .218 xwOBA and 23.1% swinging-strike rate last season.

If Bundy features his slider more heavily thanks to Maddon’s quick hook and fewer starts against the same hitters, then he may flirt with a 4.00 ERA. 

Other factors to consider

This upcoming season is unique for six-man rotations. Although extra rest doesn't appear to have a significant effect on pitcher performance on its own, pitchers may throw harder when the extra rest is combined with a shorter season.

Additionally -- except for teams with strong starting pitcher depth -- six-man rotations should provide added job security for starting pitchers. Each pitcher added to the starting rotation leaves fewer options for his replacement on the roster, so starting pitchers in six-man rotations have elevated job security as a result. That may be a minor factor for competing teams since returning to a five-man rotation is always an option, but non-competing teams are incentivized to see their pitchers pitch, even if they've been struggling.

Pitchers may also be better protected from injuries in six-man rotations. Fewer innings means fewer opportunities for injury, and some research suggests that extra rest can significantly decrease injury rates. Overall, most pitchers aren't likely to see significant negative effects from a six-man rotation, and some are positioned to benefit from the strategy.

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