Although I’ve yet to see the documents (the ask has been made), I’m certain that the NFL filed a case seeking what’s known as a “declaratory judgment” under the Federal Arbitration Act, explaining that a controversy clearly exists on the viability of Goodell’s final ruling in the Brady appeal and asking the court to determine the parties’ legal rights.
It’s not entirely uncommon, but it’s a very aggressive maneuver. As a practical matter, it potentially short-circuits the efforts of the NFLPA and Brady to file in Minnesota (with Judge David Doty presiding) or Massachusetts (with Judge Pats Fan presiding), where the ruling likely would be more favorable to Brady.
Whether through pre-emptive lawsuits or otherwise, forum shopping happens all the time in the legal profession. Part of securing the best outcome for a client is picking the best court for attempting to secure that outcome.