However, before anyone see this change in formulas as a sign that the Sox screwed up by letting Bay go, don't get too excited: it turns out Theo & Co. have their own formula for measuring defensive capabilities, and they saw both Bay and Ellsbury as being about average in the field. This revelation led John Tomase to conclude that Bay's time in Boston was done earlier than we initially thought:
The new UZR wouldn’t have impacted the Sox’ decision to let Bay walk. Even with the adjustments, Bay is still at minus-55.9 runs lifetime, though part of that can be explained by his 2007 knee surgery.It's an interesting conclusion, though I have to wonder if the deal still had a chance until the two parties realized they were nowhere near meeting on price.
More importantly, we now know he was as good as gone once contract talks collapsed at the All-Star break over his medicals.