I am not sure defense factors into this metric. Someone (ahem! @sveumrules) with time, interest, and more intelligence than me can correct me if I'm wrong:
BP's Stuff Pro and Pitch Pro Stats
At a high-level StuffPro and PitchPro are measures of the value of a pitch—scaled to runs per 100 pitches, with negative values favoring the pitcher—based solely on the physical characteristics of the pitch and its release, the handedness of the batter, the count in which it was thrown, and—in the case of PitchPro—the location it crossed the plate.