Napoli will play as few games behind the plate even as few innings behind the plate as humanly possible. So his catching defense is meaningless or close to it.
I am concerned with his defense at 1st base which is also not that good. My concern there is with WMB's throws which were at least last year terrible. If WMB is going to throw like that for a career he is going to need a pretty good 1st base glove over there digging his throws out of the dirt or stretching for them, left...right, up...down....all over the place. While I am on that topic WMB has so far been a defensive improvement over Youk at 3rd but in general has not so far proven to be a solid defensive 3rd baseman. As it is both Napoli and WMB might have to wear shin guards in the field.:D