Mid-summer roster quandaries: Zimmerman and Detwiler

As the Nats get ready for Bryce Harper to return next week, the team faces its first major roster quandary of this season. Over the last three weeks, Ryan Zimmerman has proved to be a reasonably good left fielder while filling in for Bryce, but now decisions will need to be made about where to play him and how that will impact the rest of the lineup.

The two main choices are to move him back to third base, Anthony Rendon to second, and Danny Espinosa to the bench, or to keep Zimmerman in left field, move Harper to center, and Denard Span to the bench.

If Zim is capable of playing third base adequately, logic argues in favor of moving him there and sitting Espinosa. Simply  put, Span is a good player and Espinosa isn’t. For example, the projections available from FanGraphs show Span with a projected slash line of .273/.323/.380 (close to a league average hitter, plus above-average defense) and Espinosa with a slash line of .221/.283/.361, which is about as low as it gets for players with significant projected playing time.

Of course, other variations could be used on occasion—Zimmerman might occasionally give Adam LaRoche a day off at first base, or let Harper move to right to give Jayson Werth a day off. But those variations, barring an injury, would be used only on occasion to keep the team rested.

So the big question is whether Zim can still play third base. If he can, I’d suggest a somewhat unusual platoon arrangement. Espinosa hits much better against left-handers, so I’d suggest playing Zimmerman at third against right-handers, and move Harper to center and sit Span against lefties. Espinosa’s career slash line against right-handers is a terrible .217/.288/.369, but against lefties it’s an impressive .266/.338/.457. Span, on the other hand, doesn’t have much of a platoon differential, but he lacks Espinosa’s power against southpaws.

The Nats’ other roster puzzle (at least to me) is their utilization of Ross Detwiler. In Tuesday’s night’s 16-inning marathon, he pitched 4 scoreless innings to keep the game tied—probably the Nats’ single most impressive relief appearance this season, which allowed Zimmerman to eventually hit the winning home run. But overall, Detwiler’s season has been pretty horrible—his opponents’ slash line of .290/.389/.442 indicates that he’s probably been even worse than suggested by his 4.36 ERA.

With the poor performance has come a willingness to use Detwiler mainly in low leverage situations when the team is either several runs behind or has a large lead. Of his 21 appearances, 14 have come with a leverage index of .75 or less (that is, a low leverage situation), with 12 of these in situations where the Nats were down by 3 or more runs or up by 5 or more runs. Tuesday’s extra-inning marathon (leverage index of 2.52) was his only appearance with a leverage index greater than 1.50. (Note—a leverage index of 1.00 represents an “average” situation.)

Detwiler hasn’t taken well to relief and still aspires to be a starter, but that isn’t going to happen with the Nationals, who have brought in Blake Treinen or Taylor Jordan when they needed a replacement starter. He’s being paid $3 million this season, which seems like a lot for a player in such a marginal role. His fasball velocity is still fine, but he relies on it too much. With a season and a half until free agency, I think it may make sense to try to trade him. Perhaps another team thinks it can succeed where the Nats have failed, in developing another pitch and allowing him to move back into the rotation. Without Detwiler, the Nats could move Treinen or Taylor Hill into the long-relief role, or bring up Xavier Cedeno as a lefty specialist. Detwiler wouldn’t bring much back in a trade, but I still think it may be better for both him and the Nats to trade him.