Opening day in doubt for Koji Uehara, who closes for Red Sox?

Koji Uehara has been out with a hamstring strain for a few days now, and with no date set for his return to the mound, Boston's closer is uncertain whether or not he'll be ready to go come Opening Day.

It took a while for Uehara to win the closing role in 2013, with fans surviving through runs from Joel Hanrahan and Andrew Bailey before the Sox found their fan in Koji. Since then, excepting a break towards the end of last year when the games no longer mattered, the ninth has been almost a foregone conclusion. Three outs, a save, and few worries along the way.

Now, even ignoring the question of just how well Uehara can rebound from his late 2014 struggles, it seems Red Sox fans might have to live without that security for the first days of 2015. Baseball doesn't wait for injury, however, meaning the Red Sox will need to find someone to take his place when the game is on the line in the ninth. Who can they turn to to take over for Koji when the need arises, both in April and for the rest of the year? Let's consider the options:

Closer By Committee

Let's get the old standby out of the way first: the Red Sox are not a great candidate for this approach. This is particularly true if we expand the role of closer to include those eighth inning moments when the game is clearly in jeopardy and a couple big outs are needed, as it has been for Uehara more than a few times these past couple years.

Closer by committee is often a fancy way of saying "we've got nothing," but sometimes it's also about best utilizing a bullpen with some very specific specialties. If you've got a couple of guys who can get you an out against a righty, and a couple who can get lefties, one who is particularly good at exploiting free swingers and another who will just throw strikes, then a manager can navigate his way through most situations with favorable matchups even if the talent isn't particularly impressive.

The Red Sox aren't particularly well-suited to this. Their lefties get righties out, their righties can keep lefties off base. The major caveat, of course, being that this is only true if they're getting anyone out. If Boston's relievers are effective, they'll probably be effective against everyone more or less equally, and there's enough talent in here that the Sox don't really need to rely on a plan like this to survive the late innings.

Anthony Varvaro

Despite the fact that he cost the Red Sox next to nothing, Varvaro is coming off two strong seasons for the Atlanta Braves, and arguably has the best recent track record of any of Boston's non-Koji relievers. In 54 innings last year, Varvaro allowed just 16 earned runs (a 2.63 ERA), striking out 50 and walking just 13. He's certainly got the raw production that might make him a good temporary closing candidate.

That being said, Varvaro was not exactly exposed to the most high-pressure situations, with only about a quarter of his plate appearances being deemed "high leverage" by Baseball-Reference, and more than half coming in at "low leverage." Those numbers get even more pronounced in 2013, where he was used almost exclusively in low leverage situations coming off a rough 2012.

Varvaro would be a solid choice just based off his recent results. The Red Sox could run him out there for the ninth without feeling helpless as they have in certain years past with players like Alfredo Aceves taking the role. But if he's not a bad option, he's also probably not the best.

Photo Credit: Brian Garfinkel

Edward Mujica

Coming into 2014, Mujica would have been the obvious choice for the role. Obviously, though, last season did not go as planned, with the one-time Cardinals closer posting a 3.90 ERA in 60 innings of work with the Red Sox.

As bad as 2014 was for Mujica, there's reason to believe his struggles won't be continuing on into 2015. Between positive peripherals and a strong positive trend to his results as the year went on, there's reason to believe Mujica simply hit an early bump in the road and, reliever sample sizes being what they are, was unable to recover completely before the season came to an end. We don't blink twice when a hitter has a couple bad weeks and then is great for the rest of the year. But for a reliever, there often enough just isn't the chance to recover from that initial rough start.

If we erase 2014, then Mujica once again seems like the natural candidate to close. He's been in that role before, and we know he can handle it. And if the candidates stopped there, I think Mujica might well be my choice for the position. But there's still another player who deserves consideration...

Junichi Tazawa

Junichi Tazawa's reputation is perhaps not all that it should be. It's not that he's distrusted in Boston, mind, just that it seems fans are not quite as comfortable with Tazawa as they should be given how fantastic he's been. In the three years since he established himself as part of Boston's bullpen, Tazawa has posted a 2.62 ERA with a 181:34 K:BB, good for a 156 ERA+. He has the 18th highest fWAR total of any qualified reliever over that period--a list which, for the record, runs some 171 names long. There aren't enough real "closers" ahead of him on that list to cover half the teams in Major League Baseball.

Simply put, if Koji Uehara is out, Junichi Tazawa is the best arm in the pen. And he absolutely has the experience in tough situations, even if he's never made his way into the closer's role. About 40% of Tazawa's plate appearances came in high leverage situations last year despite the Red Sox generally lacking for them, and in case you need to be reminded he was one of the go-to arms in the 2013 postseason, picking up some huge outs most notably against Miguel Cabrera in the ALCS.

Frankly, while Tazawa is set to hit free agency around the same time Uehara will likely retire, the Red Sox might well be getting a preview of their future closer here. Sure, there's a few good candidates bouncing around the minor leagues--Matt Barnes may well find himself in that conversation before long. But Tazawa is the closest thing they have to an heir apparent at the position. It's not an idea that's gained a ton of traction yet, but don't be surprised if the Sox start talking extension with Tazawa before too long. Or if they give him a quick audition early on in April.