People love to label phases and eras, so few periods in baseball have gone without names. The 2010 season will be known as the Year of the Pitcher, if last year’s coverage is any indication, just as the Dead-Ball Era lives on nearly a century later. If the first half of the 2011 season comes away with a nickname, history will have to choose between three compelling options: the Year of the Pitcher II, the Summer of Geriatric Managers, and the Invasion of the Six-Man Rotations. Sequels suck and demographics matter, leaving the latter as the most logical choice. The Yankees have thought about going to a six-man rotation, and the Athletics will use one—at least for a week—and when the rich and smart kids are thinking about making a particular move, then it’s time to talk about it.  

The most effective means of using starting pitchers has always been a hot topic in the sabermetric community, and it’s inextricably tied to workloads, which in turn inevitably leads back to a discussion of optimal rotation size. In Baseball Between The Numbers, Prospectus alum Keith Woolner wrote about the advantages in going to a four-man rotation—citing, among other reasons, fewer starts going to poor fifth starters and an extra roster spot (Rany Jazayerli hit on similar points during his series in 2002). Another sabermetric publication, The Book (by Tom Tango, Andrew Dolphin, and Mitchel Lichtman), also addressed the topic. Within, the trio suggests that the optimal rest period is five days, while the worst is three days—concluding that four days of rest, the amount currently employed by most teams, is a good compromise.

One common bond between these analyses is the denunciation of excessive rest. In that sense, a six-man rotation can hurt, as off-days and rainouts can lead to six or seven days off between starts. There’s an even more practical reason for the scarcity of six-man rotations. To riff on an Earl Weaver quote: it’s easier to find five good starters than four. However paradoxical it may seem, the teams most likely to expand their rotations are the ones least equipped to do so. Those teams who do make the addition tend to do so for at least one of the following reasons: 1) to evaluate another pitcher; 2) to prevent injuries; 3) to showcase a pitcher for trade; 4) to decrease workloads; and 5) to give everyone an extra day off. 

The Yankees, who have since decided against opting for a six-man rotation, have CC Sabathia at the top and follow him up with a number of inconsistent or fragile options—both, in a few cases. Going to a six-man rotation makes sense on some level for the Yankees, since it lessens the strain on those injury-prone starters. Then again, going to a six-man rotation means that instead of Sabathia making 32 or 33 starts, he would make 27 or 28. With New York paying Sabathia an unholy amount of money to complete high-quality and high-quantity innings, the last thing the Yankees should do his limit his workload without a reason other than the inadequacy of his supporting cast.

In order to maximize Sabathia’s starts within a six-man rotation, Joe Girardi and Brian Cashman would have to plot out a plan, perhaps one that would have Sabathia start every fifth day, regardless of the remainder of the rotation’s status, over the balance of the season. Otherwise, the negative effects of fewer Sabathia starts would likely equal or eclipse whatever marginal benefit the Yankees would gain by going to a six-man rotation. Losing starts by top-of-the-rotation pitchers is just one of the negative consequences suffered by teams who go to six-man rotations. It’s impossible to discuss these disincentives within the context of the Yankees, because most are budget-related, and the Yankees’ budget—while finite—often feels infinite.

Instead, consider the Braves’ situation. With Tim Hudson, Derek Lowe, Tommy Hanson, Jair Jurrjens, Brandon Beachy, Mike Minor, Randall Delgado, and Julio Teheran, the Braves could go to a six-, seven-, or even eight-man rotation if they absolutely had to. The phrasing is important there, since as long as Atlanta can choose to arrange its rotation as it sees fit, the Braves should limit their starting staff to five. By having either Beachy or Minor in the majors at any given time, but not both, the Braves can save service time for the other, thus slowing the trickle of sand through the hourglasses marked “free agency” and “arbitration.”

Another reason why teams with sufficient weaponry to do so rarely employ the six-man rotation is because it is an inefficient usage of resources. The Braves could—and some might argue should—take their starting pitcher surplus and flip a piece for an upgrade in center field. One of those positive externalities from keeping the sixth starter in the minors is that it keeps him away from displaying possible flaws that the best hitters in the world can exploit, thus preserving his trade value.

The trade value trick can work in reverse, too. The White Sox were the first team this season to try out a six-man rotation, and for them, it made sense. With Edwin Jackson and Mark Buehrle becoming free agents this winter, keeping Philip Humber around is as much about evaluating him for a role for this and next season as it is anything he might contribute in 2011. Kenny Williams is unpredictable, but it’s easy to envision him flipping Jackson or Buehrle before the deadline, and with Jake Peavy returning from serious surgery, easing him back into the flow of things wasn’t the worst of ideas. John Danks injured his oblique and required a disabled list, though, which torpedoed the White Sox’s plans.

Chicago’s idea worked in part because none of their options appeared to be horrendous. The Royals, on the other hand, are turning to a six-man rotation that features only two pitchers with an ERA+ above 90—the other four have an aggregate earned run average of 5.26. Dayton Moore undoubtedly hopes to drum up some trade interest in Jeff Francis and Bruce Chen while keeping both healthy, and limiting Danny Duffy’s innings is a smart idea. The problem is the other starters. Since the dawn of the 2008 season, Kyle Davies has a 5.20 earned run average. Among starting pitchers with at least 300 innings pitched, that ranks seventh-worst—behind Brian Bannister, Luke Hochevar (also in the Royals rotation), Charlie Morton, Andy Sonnanstine, and Ian Snell.

Moore’s squad isn’t the first team with aspirations of competing in the future to go to a six-man rotation during a lost season—the 2006 Devil Rays and 2008 Padres both went into plus-one mode in September. That’s the thing, though: this is July, not September. There is a legitimate chance that three or four of the six starters will exit the organization’s clutches this offseason (depending on whether the Royals like Felipe Paulino and Hochevar enough to hold onto them), so it has to be grating for the fans to watch mediocre performances from ineffective band-aids.  For that and other reasons, this summer trend will probably be forgotten rather than emulated in coming seasons, just as it was when the Mets tried it in 1998.

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To riff on an Earl Weaver quote: it’s easier to find five good starters than four. You mean 'than six.'
The link about the A's rotation appears to be broken. Also, the A's optioned Josh Outman after Saturday's game, so the flirtation with a six-man for more than one turn through the order may be over.
If the optimal rest period is really five days, then wouldn't a 5.5 man rotation be optimal?
Bring back the Sunday starter. "In order to maximize Sabathia’s starts within a six-man rotation, Joe Girardi and Brian Cashman would have to plot out a plan, perhaps one that would have Sabathia start every fifth day, regardless of the remainder of the rotation’s status, over the balance of the season" - would that really be so difficult to achieve?