Points per game allowed on the season: 91.1, a league best.
Points per game given up in the 27 games since the Perkins trade: 91.04.
(Toss out that Bucks' game, if you like, and it's 92.4, which would rank only behind Chicago for the season average.)
Strange how everyone is fixated on the Celtics' defense, post-trade. As Fafnir said, it's the offense that is the real source of concern.