With Fangraphs adding splits, it’s now much easier to determine how high on the priority list finding a suitable platoon partner for Colby should be (if it should be there at all). If we were to base the decision solely on last years performance, then the answer might be #1; however, as with everything numbers related we need to reconcile the small sample size problem (~115 PAs against LHPs last year). These posts (The Book, Fangraphs, Another Cubs Blog) run through the methodology behind estimating hitter platoon skills, and the Another Clubs Blog post links a spreadsheet calculator. Running Colby’s history and his CHONE projection for next year through that methodology yields a projection of
|Proj wOBA||wOBA v LHP||wOBA vRHP|
Clearly this projection shows Rasmus being below average with the bat against LHP next year, but what’s the magnitude of that when you combine it with his above average D? And is there an option out there that could help? Those questions can be answered using a WAR v LHP Metric as in the below table. I’ll also include a couple of other potential (either still or at the beginning of free agency) platoon partners so we can get a feel for the potential gain of a platoon.
|wOBA v LHP||ORAA||DRAA||RAA|
The wOBAs were derived using the same methodology as noted above and the DRAA are prorated versions of my projections (linked on sidebar). This chart shows that a platoon would be an OK idea to the tune of about a 5 run gain. The built in assumption is that Baldelli could stay healthy enough to take all of the PAs vs LHP. Also of note, Rasmus’s splits were much smaller in his minor league days (in fact, including the MLEs for his last two years in the minors would bump the projection up to 0.306).
So what’s my final answer? If Rasmus needs a day off, then obviously giving it to him against a LHP is a good idea; however, the marginal gain (at most ~5 runs) probably isn’t enough to get worked up over if the Cards don’t bring anyone in to platoon with him.