Just to be the turd in the punchbowl, I'll note that the Celtics are getting outscored by 5.8 points points per 100 possessions with Brown on the court since the new year. In that same time frame, they've been +9/100 with Brown off the court. (Those numbers are -2.8 with Brown, and +7.3 without if you want to look at only February onward).
went to NBA.com and sure enough, JB is in 8 of the worst 11 lineups by +/- since Januray 1. But here are the lineups followed by total +/- , games, and minutes.
J.Brown, A.Horford, K.Olynyk, T.Rozier, M.Smart = -13 (6 gp / 12 min)
J.Brown, J.Crowder, A.Johnson, M.Smart, I.Thomas = -11 (5 gp, 13 min)
J.Brown, J.Crowder, A.Horford, T.Rozier, M.Smart = -10 (1 gp, 2 min)
J.Brown, A.Horford, K.Olynyk, M.Smart, J.Young = -9 (1 gp; 7 min)
J.Brown, J.Crowder, A.Horford, J.Jerebko, I.Thomas = -8 (5 gp; 25 min)
J.Brown, J.Crowder, J.Jerebko, K.Olynyk, T.Rozier = -8 (5 gp; 9 min)
J.Brown, G.Green, J.Jerebko, K.Olynyk, M.Smart = -8 (2 gp; 3 min)
J.Brown, J.Crowder, M.Smart, I.Thomas, T.Zeller = -7 (2 gp; 6 min)
J.Brown, J.Crowder, A.Johnson, K.Olynyk, I.Thomas = -7 (1 gp; 3 min)
To me, there are some funky lineups there that don't have a lot of minutes. Perhaps more encouraging is the starting lineup - J.Brown, J.Crowder, A.Horford, A.Johnson, I.Thomas - is +10 in 69 minutes (7 games).