Not really. There may be some merit to combining metrics like UZR and PMR, but they mostly have to do with increasing the validity of the observed measurement. But on the whole, you're better off using the best defensive metric available, rather than trying to combine the results of all defensive metrics. In this case, RZR is the best defensive metric we have available to us for Year 2008 performance. (Jinaz does a great rundown of what's available, although it predates the release of several promising Retrosheet-based methods.) I don't mean combining them, I mean looking at each one critically for agreement If I have a measuring tape that measure in only inches and something measures to 14 inches plus some undetermined extra and I have another tape that measures in in 1/2 inches and it measures that same thing 14 inches and something less than 14 1/2. If there's a third one that only measures in centimeters and it measures 36 cm, I still don't know what the exact measurement is but I'm willing to bet it's right around 14 inches. If multiple defensive metrics say that Theriot isn't doing well, he's probably not.