[Update: 5:22 pm] The Red Sox are not shutting Doubront down to limit his workload, but they are skipping his next start, in favor of Aaron Cook, in order to at least slow down the innings total and give him a breather.
Following Thursday night's 4-1/3 inning outing against the Cleveland Indians, Felix Doubront is now just 6-2/3 frames shy of matching his professional career-high workload. In 2008, splitting time with Low-A Greenville and High-A Lancaster, a 20-year-old Doubront threw 129-1/3 innings in what was easily his most successful pro season to date. Now, he's at 122-2/3, succeeding in the majors as a back-end rookie hurler, but at some point a question has to be asked about how much is enough in 2012.
His 4.70 ERA isn't amazing, but once you adjust for park and difficulty, you end up with an ERA+ of 94. That's a little below-average, but for a fifth starter that the Red Sox are paying the league minimum, too, that's fine. For comparison's sake, John Lackey posted a 99 ERA+ in 2010, but at an $18.7 million price tag in the first year of a long-term deal. Doubront's roughly $500,000 check looks far better in that light.
It's not exactly the same, though, as Lackey also threw 215 innings, a figure that has plenty of value by itself. Doubront isn't going to come close to approaching that workload, as even if he picked up another eight starts in 2012 and threw six innings each time out, that would put him around 170 innings. Doubront has to work to that point, where he can contribute value simply by showing up to start, and shutting him down too early will work against that goal.
Boston has been relatively careful with Doubront's pitch counts, as he's averaged 99 per outing over his 22 starts. Since June 8, when he was removed after 82 pitches in four innings, Doubront has tossed 96 per start, so Boston isn't ramping up his workload as the year progresses -- he had four starts of at least 108 pitches in his first 11, and just two since. With the bullpen Boston has in place, they can afford to shave an inning of here or there for Doubront in order to keep the overall workload down, and that's why you see thing such as Clay Buchholz with more inning on the year despite three fewer starts.
There's no need to outright shut Doubront down, as you're just going to have to go through this process again in 2013 if you don't ever ramp up his workload. As it is, he's 24 years old and yet to crack the 130 inning barrier. As he's averaging roughly 5-2/3 frames per outing all year, and closer to 5-1/3 over his last 11 starts, chances are good that a Doubront that stays in the rotation for the rest of the season will finish around the 160-170 mark, depending on if the Sox do shut him down in late September or not.
That's a very good place to finish with him, as even though he's struggled far more as of late in his first year as a starter, you're not going to make him any more capable in the second half without continuing to pitch him. And it's not as if tossing 160 innings would represent an enormous increase from his previous career-high as a professional, so the Red Sox can continue to use their fifth starter without putting Doubront's future in danger. And, since the only real replacement around is likely Aaron Cook, unless Boston acquires a starter through a waiver trade, it's not going to hurt their present day, either.
Doubront won't have any serious value to the Red Sox as a back-end starter until he can start to throw enough innings to make a roughly average performance worth their time. He's potentially useful right now, and has thrown some very impressive outings, but also mixed in plenty of poor ones, and just hasn't shown the stamina to be relied upon in the seventh, or, in many starts, even the sixth. Cutting him off now won't help that, nor will stopping him from starting in another week or two. Let the kid throw, continue to monitor his pitch counts in the process, and prepare him for what will hopefully be a stronger 2013 effort.