Quantitatively it takes longer to evaluate? I think it's pretty clear some guys are good fielders right when they come up, I'm sure you'd agree. So for example, I think Gose is a pretty good outfielder but fangraphs says otherwise for this season (as we saw evidently last weekend). If the statistics or actual results are pretty volatile, teams might be risk averse and offer lower contracts to good defenders. So not really a market inefficiency.