I've read most of the brief that the NFLPA originally submitted. It seems to me like they've got a very strong case re the arbitrator lacking impartiality and lack of notice for the punishment (i.e. not based in the CBA).
As I understand it, the NFL's position is essentially -- the court has to give deference to the arbitrator, Goodell had a right to be the arbitrator, and so the court must basically affirm the decision that he made as arbitrator.
The NFL's position is a strong one, but I think they're asking for a really, really generous interpretation of the league's powers under labor law. More or less a rubber stamp of any decision they choose to make. Some judges probably would side with the NFL. I hope Berman does not.
But hey, I'm a pro-labor liberal, and a Pats fan to boot.