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UZR can't normalize for teammates. By definition, if a good fielder takes a ball in a bad fielder's zone...it's a miss for the bad fielder an OOZ play for the good fielder. The good fielder steals credit from the bad, resulting in an amplifying impact on the results. Two good fielders side by side will be stealing lots of plays from each other...both of their lines will go DOWN relative to what they would be with an average fielder for a partner.
I think I will make this my top priority if ever I get any time to do more stat analysis