I disagree. If we applied a modified pitch f/x system that used high-speed video to track the movement of every moving part on the field, we absolutely could get to the point. We would know the precise speed and trajectory of any ball, we would know the fielder's position at the time of the hit, we would know how long it took them to not only break to the intercept but also how long it took for them to receive and transition to the throw, so on and so forth. for every single play. no more relying on human subjectivity, no more guessing, no more unknowns. They are working on this, called field f/x. I may be getting it confused with hit f/x but I believe they have it at Pac Bell and maybe one or two other stadiums but only mlb has access to the data. Until they make this info available, the best we can do use UZR, +/-, and scouts create a best estimate of a players defensive value.