The idea for this post came from reading Sons of Sam Horn, specifically this thread about the starting pitching staff and the pitchers roles on the team. The line about the Loch Ness Monster though, that was all me.
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Imagine a pitcher who sits in the bullpen. It's the third inning and the game's starting pitcher has just been injured. The bullpen phone rings and the pitcher in the bullpen is called into the game for several innings. He throws two or so and then in five days when the injured pitcher's turn in the rotation comes up he gets the start. He's not the love child of Dennis Eckersley and the Loch Ness Monster, so he isn't perfect, but he's perfectly serviceable in both roles. Were he a super hero, his special power would be flexibility. No, not like that. Gross.
I do believe starters are more valuable than relievers because they throw many more innings. For that reason I think the Red Sox blundered by not moving Aceves to the rotation in September where he could make a bigger impact on a team starved for decent pitching. Were the season being played now the equation would be different. In the middle of the season finding talent to plug into the rotation is much more difficult and costly.
But it's the off-season, meaning there are options galore. There are many starting pitchers and relievers about to go on the market, and the Red Sox, like all teams, can sign who they like. If the Red Sox plan for it, Aceves can give the Red Sox a sort of 'free' starting pitcher, one who relieves most of the time, but can step in and start games on a moments notice without the organization having to start dredging out the sludge from the AAA rotation. That ability to start or relieve and to bounce back and forth between the two is why Alfredo Aceves should remain in the bullpen for the 2012 season.
Putting Aceves into the rotation now means the team either has to find another pitcher with his flexibility who can both start and relieve and is willing to sign with Boston knowing that is his role (not likely) or lose that flexibility and sign an extra starter to stash in AAA in the event of injury. The quality of a starter who would accept an assignment to AAA would likely be less than what Aceves could provide, so unless there was someone else to step in, we're talking about a drop in quality on the mound for some number of innings.
The Red Sox can find starting pitching almost as easily (if not as cheaply) as they would relievers. Playing it that way gives the team an easy in-house replacement should an injury arise.
Yes, it would likely be easier and possibly even cheaper for the Red Sox to put Aceves in the rotation and find a relief pitcher this off season, but that would cost the team in-season flexibility. We've all seen the damage to a starting staff wrought by a full season of baseball up close and personal. The flexibility that Aceves brings, the ability to plug a huge leak effectively on the fly, would be blunted by placing him in the starting rotation. Doing so while there are other options available doesn't make sense.