Word came down today that Grant Balfour would be missing four to six weeks with an injured knee, on which knee surgery has already been performed. That linked story (from Susan Slusser, of course) relays a variety of quotes saying things like "I won't be surprised if he's back even earlier" and whatnot, but the real story, in my opinion, is that this just doesn't matter that much.

Happily, if you're a Baseball Prospectus subscriber, PECOTA has hit, which means the patented (not really) BP depth charts, powered in large part by the inimitable Jason Martinez of MLB Depth Charts, have also hit. This provides an easy, at-a-glance look at the makeup of the A's bullpen.

Here's a short version:

Balfour: 2.78 ERA
Doolittle: 2.43 ERA
Cook: 4.53 ERA
Blevins: 3.70 ERA
Neshek: 4.34 ERA
Resop: 3.99 ERA
Rodriguez: 4.88 ERA

Nobody's sure who the closer will be in the absence of Balfour. If it's Doolittle, then PECOTA actually thinks that the A's will be better off, though there's plenty of room for doubt in that projection, in part because Doolittle was a one-pitch pitcher last year and in part because Doolittle has thrown a grand total of 73 1/3 professional innings, so it's hard to get a handle on just how good he is.

Even if it's Cook, though, let's call that a two runs per nine innings difference in their expected runs allowed. But a reliever of this type only pitches an inning at a time, so we can also think of that as two runs per nine games. And of course that's not per nine A's games but per nine games that the pitcher pitches, which in this case means save situations.

If we add six weeks to today's date, that takes us to Thursday, March 28. On that day, the A's are schedule to play the Giants at AT&T Park. In an exhibition game. They won't play their first real game until April 1st. But suppose Melvin wants to ease Balfour back in and use him in a middle relief role until April 9th. The A's have seven games before that date. If they face the same number of save opportunities that they did last year (64), then there's about a 40 percent chance of having a save chance in any given one of those games. (Though that's without any further information, like how you're more likely to have a save opportunity if your pitcher is a good one because you're more likely to have a lead period.) So if you're looking at two to four of those games presenting save chances and expecting to allow an extra run every four or five games and remembering that plenty of save opportunities are two- and three-run leads, well, you can pretty easily come to the conclusion that the expected impact of this injury, even if Balfour takes the full amount of time to come back and isn't ready to close when he does return to active duty, is minimal at the closer level.

Of course, when a reliever goes down, you get cascading effects. The makeup of this year's bullpen, though, and PECOTA's expectations for those pitchers, is such that those effects also seem small. If Doolittle ascends to the closer role, then Blevins becomes a setup man, perhaps, and you're losing a run every nine games in the seventh or eighth inning (plus whatever you lose from bumping ... Pedro Figueroa (?) into the Blevins role, though the leverage of those innings would hopefully be quite low), but Doolittle, at least by PECOTA's lights, doesn't cost you anything at closer.

And if Cook is the closer and you get Neshek or Resop or Rodriguez stepping up to his setup role, then whatever you're losing at closer (again, per PECOTA), you're stopping the buck there because whoever steps into Cook's innings is expected to be just as good as he is.

Honestly, though, all these projected ERAs are fluff in this piece, because the real story is the calendar: four weeks or five weeks or six weeks or even seven weeks or eight weeks just doesn't leave Balfour missing very many games.

Any time a pitcher injures a leg or something non-arm-related, you'll get people, sometimes managers, sometimes bloggists, saying things like "well, at least it saves wear on his arm," and this injury is no exception—travel back over to that Slusser story and there's Melvin quoted saying exactly that. It's a cliche at this point, but in this case, it's hard to escape the conclusion that it's true.