The World Series champion Chicago Cubs earned that title in part because of their careful handling of their starters' workloads down the stretch last season. They'll look to defend that title with a similarly unorthodox-but-understandable arrangement in 2017.
Joe Maddon has been talking about a "hybrid" setup in the back end in which Mike Montgomery and Brett Anderson either rotate in and out of the No. 5 spot or elongate the starting staff to a sixth spot. For the Cubs, in this particular moment -- with Anderson and Montgomery having never pitched a 200-inning season and with Jon Lester, Jake Arrieta, Kyle Hendricks and John Lackey all having pitched deep into October -- rethinking the rotation alignment makes sense. And over the years, we've seen many other clubs temporarily venture away from the traditional five-man for brief periods out of necessity or in deference to scheduling quirks or particular player circumstances.
But at a time when bullpens have taken on added prominence, when teams are still trying to come up with creative ways to limit pitcher injuries and when the schedule itself is on the verge of an adjustment, it's worth wondering if a real evolution away from the five-man model is possible.
"In the long run, I'm sure we'll see some kind of change," Rays vice president of baseball operations Chaim Bloom said. "A lot of the things teams are trying now are just better ways to deploy the guys that they have to maximize the number of games they win … The question is how can you build something that can hold up for 162 games or 180-plus days?"
Because ballplayers, like most human beings, are resistant to major change and a grassroots revolution takes time, the five-man rotation does not exactly have a pressing expiration date.
But there are arguments for and against altering the standard five-man model in the here and now.
Let's explore them.
The four-man rotation
Once the norm, four-man rotations became less common in the 1970s, after the Dodgers popularized the five-man with Tommy John, Don Sutton, Burt Hooton, Rick Rhoden and Doug Rau. Teams will still use the four-man when off-days allow, bringing back their ace on regular rest and skipping their No. 5 man. But a true four-man unit has been effectively extinct since 1975.
"When I first went to Arizona [in 1998], we were going to try to go to a four-man rotation," Orioles manager Buck Showalter said. "The problem we ran into is it would have to be completely self-contained. A free agent wouldn't sign with you if you were using that format. So that kind of threw it out the window."
But it's a different game than it was in '98 and certainly than it was in '75.
In '75, relievers accounted for 27.2 percent of all innings pitched. In 2016, it was 36.7 percent. Eight-man bullpens have been increasingly in vogue, at the expense of the bench and not the starting staff. But a four-man rotation would allow teams to potentially take the relief evolution even further with nine-man bullpens that allow for aggressive hooks and more of a matchup mindset.
Putting starting pitchers on a three days' rest regimen would compel clubs to limit their pitch counts and innings. But to a certain extent, that's already happening.
Just in this decade alone, the average number of pitches per appearance by Major League starters has dropped from 97.0 in 2010 to 92.6 last season (the lowest average STATS LLC has on record, going back to 1988). The average number of innings per start hasn't been above 6.0 since 2011, and it was 5.7 last year.
In 2016, there were just 15 pitchers who accumulated 200 innings -- the fewest of any non-strike-shortened season.
"If you have a strong, deep bullpen, and you carry 13 pitchers, there is a little bit of an understanding that you can have some five- or six-inning starters," Astros manager A.J. Hinch said. "That 200-inning threshold has softened a little bit -- not in the minds of pitchers but in the strengths of teams."
A four-man unit would force teams to place greater limitations on those very few starters who qualify as absolute aces, but it would also increase the number of games in which those aces appear. For pitchers of all pedigrees, it would reduce the threat of the "third time through the order penalty." (Last season, opponents' OPS marks went from .718 the first time through the order to .754 the second to .793 the third.)
"Teams are seeing the defensive value of changing pitchers," Orioles GM Dan Duquette said. "The more times the hitter sees the pitcher, the odds go more in the hitter's favor. So teams are looking at that."
They'll have something else to look at in 2018 -- a schedule with four additional off-days, as mandated by the new Collective Bargaining Agreement. That will provide more opportunity for teams to skip their fifth starter and essentially go with a four-man group for certain stretches, although some teams will inevitably apply those days toward other purposes.
"Without knowing exactly what [the schedule] is going to look like, the modeling would allow you to protect who you feel you need to protect," Cardinals GM John Mozeliak said. "Like for us, with [Michael] Wacha, you could use those days to buy him an extra off-day or to skip starts to protect him from shoulder fatigue."
The biggest problem here would be player pushback. Even in an environment of increased appreciation for relievers, the bottom line is that fifth starters have a higher financial value attached to them than eighth relievers. A four-man rotation would seemingly limit overall earning power, and so it's not an arrangement that would be easily embraced.
The "tandem" rotation
Good on paper. Not so good in reality. That's the basic breakdown of the paired pitching model, in which the idea would be to divvy up a starters' workload to two guys.
Tony La Russa dabbled with it in Oakland in the early 1990s. The Rockies tried something vaguely similar (a 75-pitch limit on starters, with the first reliever basically going through the lineup once) earlier this decade. The Astros used tandem rotations in their Minor League system in 2013.
All of those experiments were scrapped quite quickly. The first and most obvious reason this doesn't work so well at the big league level is the 25-man roster size, which doesn't leave much margin for error. Relievers, by and large, don't have the depth of repertoire to handle more than one turn through the order, if that, and the 12- or even 13-man pitching staff operates around the assumption that starters are generally capable of eating up between five and six innings of a ballgame, on average.
"There's only so much you can do with 25 spots," Duquette said.
And there are only so many arms to go around, anyway.
"If you're doing tandems, at the rate pitchers get injured," said Braves GM John Coppolella, "you'd have to basically run 20-25 starters out there [over the course of a season]."
That's before we even get into the financial implications of any change that would fundamentally alter pitcher statistics and, therefore, necessitate a total shakeup of the arbitration and free-agent marketplaces.
But because of that aforementioned improvement hitters show the longer a pitcher stays in the game, this has always been one of those ideas that is fascinating, in theory.
Of course, to even bother trying it you'd have to have a starting staff that is, um… how can we put this delicately?… sub-optimal. And realistically, what Major League ballclub would have a starting group so sub-optimal that it's even willing to try …
Well, hello, 2017 San Diego Padres!
"We've explored about every idea internally that's possible," Padres manager Andy Green told the San Diego Union-Tribune.
The Padres are mulling over the idea of a twist on the tandem -- using an "opener" for an inning or two before bringing in a preferably opposite-handed starter, thereby possibly putting the opposing lineup in some platoon disadvantages.
Obviously, only a team with a less-than-earnest contention effort would even think to try something like this, and odds are it would be as short-lived as the other tandem experiments. But it would be interesting to watch, if nothing else.
The six-man rotation
The argument for expanding rotations is pretty simple, really. The fact that Tommy John is known more for the surgical procedure that bears his name than his role in that aforementioned five-man rotation with the Dodgers says a lot.
Going off Jon Roegele's database, over the last five completed years, there were an average of 110 reported ulnar collateral ligament replacement surgeries involving players affiliated with a professional club. Combine that with the other assorted arm-related pitching ailments -- shoulder issues like Wacha's and elbow inflammation and other maladies -- and you've got an industry that is still struggling to keep its pitchers healthy.
Would a six-man model help? The relative brevity of this list of pitchers known to have had Tommy John surgery in Nippon Professional Baseball, where pitchers are typically given five or even six days' rest between starts, would lead you to believe so.
Though the distinct difference in surgical intervention is certainly cultural, the high incidence of elbow issues for pitchers like Yu Darvish and Masahiro Tanaka after they've come to MLB from NPB and been placed in our every-fifth-day pitching plan is enough to lead you to wonder if we're doing it wrong.
Of course, therein lies the rub. To have a six-man rotation, you first must possess six healthy and effective Major League pitchers.
Some teams have a hard enough time coming up with five.
"You can talk about [a six-man setup] more readily in the Minor Leagues," said Toronto GM Ross Atkins, "because winning isn't quite as important."
Six-man rotations currently evolve only out of particular preconditions, and it could be that more teams do as the Cubs of 2016 did and stretch out their starters in the second half of the season. Atkins' club used a six-man in the second half of '16 as a means to keep young Aaron Sanchez in the mix for the full season after his conversion from relief work.
"Given the circumstance we were in and the alternatives we had, it made sense in the moment," Atkins said. "But consistency is such an integral part of this game that I don't think that's something the Toronto Blue Jays are going to consistently move toward. We feel strongly about consistent routines."
So do pitchers. With a strong stash of starters, several of whom are coming off surgery, the Mets might profile as the ideal six-man candidate in the present tense, but we all remember the stink Matt Harvey raised when the club went with a six-man for a time in 2015.
"You'd have to get six starters who were willing to live with that arrangement," Mets GM Sandy Alderson said. "The other thing is a six-man rotation is very taxing on your bullpen. So you'd almost have to go with a full bullpen as well, which leaves you a man short on the bench. It's hard to sustain that over a length of time."
When MLB and the Players' Association did not come to agreement on a 26th roster spot in the new CBA, they probably squashed -- at least temporarily -- the thought of a six-man rotation becoming a new norm.
Ultimately, be it expanding current rotations to six or shrinking them to four, changes of this magnitude -- much like rule changes -- are best experimented with at the Minor League level before implementation in the Majors. In recent years, we've seen the Astros play with a piggyback model in their farm system, and several teams, including the Cardinals, have utilized true six-man setups in their rotations in the low levels.
"The research and development of this at the Minor League level is crucial," Mozeliak said. "Because if we can show usage and why we're doing something down there and that it's still effective and that the player feels they're growing, that's a good thing."
Until then, for everybody but the defending champs and possibly the Padres, the traditional five is very much alive.
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Anthony Castrovince is a Sports on Earth contributor, MLB.com columnist and MLB Network contributor. Follow him on Twitter @Castrovince.