I believe the CBA has a clause that says something like all arbitration procedures must be completed before a court filing can be made or something like that. The NFL prefers to file in New York courts where they typically get favorable rulings, but the NFLPA jumped ahead to file in Texas before the procedures were completed and that is what the NFL is complaining about. That said, it is very suspicious that the appeal arbitrator, Harold Henderson, purposely waited until after the court announced their ruling just so they could claim it was done premature.
It has basically been gamesmanship on both sides throughout this whole process. The NFL showed their tactics against the NFLPA during last year's Brady court battle, so the NFLPA learned from that to make better strategical decisions this time and the NFL has been playing catch-up ever since. The main reason the NFL didn't try to change their strategy is because they won last time and they got what they assumed was an iron clad precedent when the courts ruled against Brady and the NFLPA last year by saying the CBA gave the NFL absolute power and control over player discipline.
However, in this case, the NFLPA didn't argue the NFL overstepped their authority. Instead, they are arguing the NFL conspired to manipulate the process by excluding evidence that went against the NFL's claims and also keeping information from the defense and the NFLPA as well. In other words, the NFL learned they may have just undermined their own iron clad ruling from last year not just in this case but also going forward as this could easily negate or restrict the NFL's authority and power over player discipline going forward, where just a few months ago, the NFL likely felt that was an impossible outcome.
Now, the NFL and the NFLPA are both in a fight to the end because there's a lot more at stake than just this one suspension. Not only could the NFL lose their power over the players, they could also lose the most important leverage they have going into the next CBA negotiations.
The NFL still has time to let this go before they risk losing that leverage completely, but even if they do drop the case, all future suspensions will already have a cloud of doubt over them and the NFLPA is likely to take more and more of them to the courts than they would have prior to Elliott's case. I think the NFLPA does not want the NFL to drop it at this point because they believe, and rightly so, that the NFL screwed up big time with this case and this is probably the NFLPA's best chance to undermine or severely restrict the NFL's authority on player discipline and quite possibly force the NFL to relinquish control of it to a real third party.
