Edward Mujica is not the kind of reliever who gets a lot of chances to be a closer. His velocity would be unremarkable if he were left-handed; his value is tied up in the unsexiest possible reliever asset, strike-throwing. According to Gameday—I wasn't able to watch—he threw nine splitters and no fastballs in the game that secured him his closer-by-default status. He's the kind of pitcher who develops, if he's lucky, a reputation for doing exactly what he did on Thursday: Coming into an inning with runners on base and getting out of it without the threat of further baserunners.
But the Cardinals' bullpen this month is exactly the sort of primordial-closer-soup in which guys who end their careers with one-or-two-hundred saves develop. Jason Motte is gone, the non-veteran competition hasn't impressed, the veteran has come off a surprisingly good season and suddenly seems like the Last Dependable Man—it's Ryan Franklin (84 saves) territory, and Edward Mujica is better than Ryan Franklin.
But Mujica's competition is probably better than Franklin's competition. So how long will Mujica remain closer?
Complication One: Until Jason Motte comes back
Nobody's expecting much out of Jason Motte now that we know he's got a torn UCL, but he hasn't had the surgery yet. When May 1 rolls around, and Motte and the Cardinals decide whether or not surgery is necessary, we'll also know whether there'll be an Established Closer lurking over the proceedings.
Complication Two: Until Trevor Rosenthal looks better
Granted: Trevor Rosenthal has struck out 11 batters in 10 innings, against one walk. But his highest-leverage games haven't gone especially well so far, and that's the kind of thing that can get you stuck behind Ryan Franklin for a while.
But he's still Trevor Rosenthal, who's generated all the vague-prospect-good-feelings that Shelby Miller and Colby Rasmus and Brett Wallace never really could, and a lot of being closer is about generating vague good feeling.. If Mitchell Boggs has a really good couple of months while Mujica is perfectly cromulent, I think Mujica keeps the job. But an exceptional month from Rosenthal and a hiccup like the one that ended Fernando Salas's fantasy baseball career could do it.
Complication Three: Until he allows a bunch of home runs
Mujica's home run rate, since he became established as a reliever, is 1.2 per nine innings. That's despite a career spent mostly in San Diego and Miami and an NL relief average of 0.87 last year. This is the last and weirdest thing about Edward Mujica, Closer: He's born to allow the occasional back-breaking home run.
The good thing about a back-breaking Jason Isringhausen blown save, for instance, was that it didn't happen all at once. He'd walk two batters on 20 pitches, fall to 3-1 against another guy, sigh visibly, strike two batters out, and allow a squib base hit over Aaron Miles's head, and while that meant you were constantly on edge during an Izzy save, you were also pretty used to being on edge by July.
Mujica's blown-save skill-set is retiring two batters with three pitches and giving up a 450-footer to Joey Votto.