'Tis the season for ambitious plans, often with short shelf lives. If it were easy to reinvent the game, the game would be reinvented more frequently, and so it is that against-the-grain ideas that emanate in Spring Training often get squashed by the realities of the regular season.
Every once in a while, though, there's a bold approach that actually starts to stick. And there's something brewing with the Tampa Bay Rays that is worth giving a particular dose of attention in 2018.
We already knew the Angels and Rangers could both experiment with a six-man rotation this season (and we've heard some pretty pronounced pushback from Texas ace Cole Hamels on the idea). But on Wednesday came word of an idea by the Rays that goes the other direction and actually makes way more sense in the sport's current climate:
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A four-man rotation.
Kinda.
The "kinda" caveat comes in because the plan, as Rays manager Kevin Cash explained to reporters, would involve a "bullpen day" every fifth day, as opposed to a schedule in which starters routinely work on three days' rest instead of the now-traditional four.

For starters (no pun intended), let's first point out that as revolutionary as this idea might sound, the four-man rotation is more retrogression than progression.
Wizened baseball historians (i.e. people who were alive in the early 1970s) can tell you that the four-man rotation was once the ordinary alignment in the Major Leagues. It wasn't until the Dodgers popularized the five-man model -- with Tommy John (the guy, not the surgery), Don Sutton, Burt Hooton, Rick Rhoden and Doug Rau -- that what we now know to be the norm truly took off. The four-man unit was basically extinct by 1975.
In 1975, starters were born to run ('75 Springsteen reference very much intended). There were 57 guys (or 2.4 per team, on average) who accumulated at least 200 innings, and relievers accounted for 27.2 percent of all innings pitched.
Last year, starters were born to get run. Just 15 of them (or 0.5 per team) went 200 innings, and relievers covered 38.1 percent of innings pitched.
We've come to think of 100 pitches as this magical mark when starters begin to wear down and get pulled. But now, even 100 pitches from a starter is becoming rarer territory. Last year, there were only 1,576 times that a starter went that deep into a game -- the lowest total in a full season since at least 1988 (as far back as Baseball-Reference's Play Index has reliable pitch-count data).
This is why eight-man bullpens are increasingly in vogue (the Phillies are even considering going with a nine-man bullpen at certain stretches this year, despite playing in a league that, because of the plentiful pinch-hit opportunities, calls for a deeper bench).

The expansion of bullpen personnel and usage is just one reason why the six-man rotation makes so little sense on so many clubs. There just aren't enough roster spots -- or, for that matter, quality starters -- to go around. The 2017 season featured just 40 qualified starters with ERA+ marks that rated as at least league average (100 or better) -- the lowest total since 1945, when there were 14 fewer teams.
So good luck finding six guys actually worthy of consistent starts.
The four-man model, however, is starting to make a heck of a lot of sense. Not just for the Rays, and not just because of the way bullpens have gained prominence.
This season marks the beginning of a new, Collective Bargaining Agreement-dictated increase in off-days -- basically, four per club per month, on average. This -- to say nothing of the change to a 10-day disabled list that was implemented last year -- will allow for teams to change the rest patterns of their starters.
Of course, you'd have to have players on board with the concept. And when I surveyed some execs about the four-man rotation idea last year, one potential problem that came up was that fifth starters typically have higher financial earning power in the open market than eighth relievers. Very true. Although, given the way this offseason has played out -- with relievers flying off the shelves around the time of the Winter Meetings and the starting market still relatively stagnant at this late stage -- this, too, might be evolving.
To be clear, a change in rotation structure must be personnel-driven. Not change for the sake of change. The Washington Nationals, for example, have three guys (Max Scherzer, Stephen Strasburg and Giovany Gonzalez) who finished in the top six of the NL Cy Young voting last season. Changing their schedules and/or limiting their workloads would be senseless.
But a team like the Rays could totally give this a try. And they could do it without the bullpen day, too.
Yes, the Rays have an established ace in Chris Archer, but he is perfect evidence of the "third time through the order penalty" that can plague so many pitchers. Archer's opponents' OPS over the last two years is .616 the second time through the order and .785 the third. League-wide last year, opponents' OPS marks were .724 the first time through the order, .783 the second and .801 the third.

Imagine, then, a scheduling setup in which Archer and his young rotation mates are limited to two turns through the order essentially every fourth day (three days' rest), with the bullpen covering the rest. Scheduling change aside, it's really not hard to imagine such a thing, because already the 2017 season saw the fewest batters faced the third time through the order (27,692) in a full season since 1976 -- back when, as we've already established, the five-man rotation was but a baby.
In other words, the limitation of starters' game-by-game workloads -- and the increased reliance on the bullpen -- that would accompany a four-man rotation is sort of already happening organically.
Maybe we're getting closer to a point where some club just makes it official.
The 2018 Rays are not that club. Or at least, not yet. The plan they're rolling with involves the usual four days' rest for starters and bullpen days sprinkled into the schedule. A reporter asked Cash if his club is being "innovative" with this idea.
"Only if it works," he said. "If it doesn't, it's dumb."
For now, it's simply worth watching. It's pretty hard to imagine a six-man rotation getting league-wide traction in times like these. But the four-man model is a throwback that might actually push the game forward.