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Agreed with RP-R Koji Uehara to a one-year contract worth $4.5 million. [12/6]

Among other problems infecting the team, last year's Boston bullpen ranked 13th in baseball in TAv Against. The Red Sox took an incremental step toward improvement by signing Koji Uehara.

Incremental because, since coming over from Japan four seasons ago, Uehara has landed on the 15-day disabled list four times and made the 60-day once. His hamstring has been a reoccurring issue, and last season his shoulder gave him problems. So the issue has been keeping him on the mound, but when he’s made it that far he’s pitched very well. In three seasons as a reliever, Uehara has struck out more than 11 per nine innings, despite a fastball that rarely brushes against 90 mph. He gets batters out with pinpoint control of his fastball and by collecting whiffs—on a whopping 40 percent of swings in 2012—with his split-finger. The combination has been equally effective against left-handed hitters in his career (.204 TAv) as against same-sided guys (.183 TAv). Since his switch to the bullpen in 2010, his peripheral numbers have held steady, even as had moved from mid-30s to late-30s.

Perhaps the most amazing thing about Uehara is that he very rarely he grants ball four. He’s walked 29 hitters in four seasons, covering 212 innings. As a reliever he’s been even better: 17 free passes in three seasons. That’s silly. The end of the story is that lots of strikeouts and few walks without a platoon split makes for a good pitcher in any role.

If there is a concern beyond health it’s a predilection for the home run. Uehara doesn’t blow batters away with stuff, so if he misses his location he will likely pay for it. Boston isn't kind to this sort of flaw, but neither is Texas, and Uehara was very effective there despite allowing a dozen homers in a year and a half. It takes a lot of home runs to undo a strikeout-to-walk ratio over 16, it turns out.

Unless Andrew Bailey gets attacked by an angry squirrel or steps on a tic-tac, he should return to his role as the closer. This pushes Uehara into a battle with Junichi Tazawa, Alfredo Aceves and Mark Melacon for the late innings role in Boston’s pen. If he’s healthy he’ll probably slot into the seventh or eighth inning. If there is one thing Boston has right now it’s money, so giving $4.5 million to someone who may or may not pitch very often won’t hurt their bottom line. Getting a pitcher as effective as Uehara, and particularly as effective against lefties, for a one-year commitment is a coup in the current environment. This isn’t the kind of move the Red Sox could make last season due to restrictive payroll commitments, but this season it’s the kind of upside play the Red Sox should make. 

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Noting here that an earlier version of this story misstated the Red Sox bullpen performance relative to the rest of the league.
I'd be surprised if Aceves throws much for the Sox in 2013. His 2012 was terrible and distracting.
I don't necessarily disagree, but the Red Sox seem to like Aceves more than I and, dare I say, you. It's possible it's an act to increase his trade value, but I'm expecting him to be a part of the 2014 roster in some role or another.