If one sorts the current Phillies by dWAR on Baseball Reference it does have Castellanos as the team's worst defensive player so far this year (-0.4). As Z said, he has been consistently below average in the OF. Usually around -1.0 dWAR for a year.
The Phillies ranking is not a surprise. Our positive players defensively so far are Realmuto (+0.4) and Segura (+0.2) with a trio of players with a small sample size +0.1 (Quinn, Camargo, Stubbs). No idea if that will hold up but Camargo seems pretty good. I do think Quinn is better than Herrera though curiously the manager has been putting Herrera in CF when the two are together - probably going for stability with Herrera who will get the most time there.
The Phillies negative defensive players are no surprise. Castellanos (-0.4), Hoskins (-0.3), Bohm (-0.3), Harper (-0.3), Gregorius (-0.3), and Herrera (-0.2). Schwarber grades a bit better than Castellanos (-0.1) though his arm looks weak so he would probably be worse than Castellanos in RF. Bohm's rating probably is colored by the 3-error day though the reality is he is likely below average there even if he cuts down the errors.
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