From what I've seen, Duran hasn't missed any catchable fly balls. I've seen Renfroe miss a few, and of course JD and Cordero, and remember a couple deep drives over Kike or Verdugo when they didn't look so good early on.
With apologies to Christian Vazquez -- who NESN tells us was recently voted the AL's best defensive catcher (Sal Perez, anyone?) -- the outfield has been the Red Sox' defensive strength this year. Maybe someone can explain dWAR: Duran and Renfroe are each -0.5; Hunter leads the league in both outfield assists and errors. JD is -0.7... Cordero is somehow better than all three, at -0.1 (no penalties for being way out of position?). The only positives in dWAR are Kike 1.6, and Dugo 0.2. In comparison: Bradley 1.1, Betts 0.3, and Benintendi 0.2.