Replacing Joe Nathan

For the past six seasons the Twins haven’t had to think about the ninth inning. If they had a lead in a close game, Joe Nathan was there to ensure victory. In only 25 of 272 instances did he fail to deliver. This year, though, the Twins will likely have to turn to someone else. News broke this morning that Nathan has torn his UCL and will probably undergo surgery before the season starts. He’s waiting two weeks to see whether rehab is an option, but at this point we can safely assume Tommy John surgery lies in his immediate future.

At RotoGraphs, Eno ran down Nathan’s possible replacements. The in-house options are pretty obvious: Jon Rauch, Pat Neshek, and Matt Guerrier. None of them stands a good chance to replace Nathan’s dependable production, but the effect on the closer role itself isn’t the Twins’ biggest problem. As Matt Klaassen has been saying all morning, they’ll lose perhaps two wins from that spot. There are larger implications, however, as Nathan’s absence cascades through the Twins’ bullpen.

For most positions, we define replacement level as the production of a AAA player called up to the bigs. This is not the case for closers. Replacement level for that position is the team’s next best reliever. When that next best reliever moves into the closer’s role, everyone else in the bullpen moves up, too. Relievers lower on the depth chart play a more prominent role. The biggest effect, then, comes at the back end of the bullpen, where the replacement level player shows up.

Teams, for the most part, can avoid using the seventh reliever on their staff in high leverage situations. But what of the former seventh reliever? He’s now the sixth reliever and will be pressed into more active duty. Such is the curse of bullpen chaining. About a year ago, Sky explained the process. His model agrees with Klaassen’s two-win estimate, but it also assumes a closer with a 3.00 ERA. The closest Nathan came to that was 2.70, and that happened five years ago. Clearly, unless one of the in-house replacements really takes to the role, as Nathan did when the Twins traded for him, the effect will be larger.

There’s no doubt that the Twins will miss Nathan’s dependable ninth inning performances. What they’ll miss more, though, is having guys like Guerrier, Neshek, and Rauch in setup roles. By moving them up in the pecking order, they’re allowing other, possibly lesser arms into the bullpen mix. That will hurt more than the mere ninth-inning downgrade.