ST. PAUL — The NFL has completed perhaps its final argument for Adrian Peterson’s six-game suspension last season, the latest attempt by the league at an off-the-field victory amid a series of legal losses related to player discipline.

NFL attorney Dan Nash made the pitch Monday to a three-judge panel of the 8th U.S. Circuit Court of Appeals, the culmination of the league’s contest against U.S. District Judge David Doty. He ordered in February that arbitrator Harold Henderson, who heard Peterson’s appeal last year, overreached his authority.

Peterson has returned to the Minnesota Vikings this season after playing in only one game in 2014, the result of the child-abuse charge he faced for disciplining his son with a wooden switch, but his case has kept on in court.

With cases ranging from Ray Rice to Greg Hardy to Tom Brady, the NFL has had several recent punishments levied by Commissioner Roger Goodell either reduced or overruled. Doty’s decision was another setback, though because Peterson can’t get the games back he missed last year the fight in this matter has come down to money and, of course, principle.

The league’s primary argument is that a judge should not be able to intervene in a collectively bargained labor dispute such as this. Nash defended Henderson’s judgment last December as fact-based and well-reasoned within the scope of the collective bargaining agreement. He accused the NFL Players Association of seeking a “get-out-of-jail-free card” with their claim that the toughened personal conduct policy could not be applied retroactively to Peterson.

“This was child abuse, child abuse that led to a criminal plea,” Nash said.

Peterson was on paid leave for nine games last season. Goodell issued the unpaid suspension in November, with six games left on Minnesota’s schedule. The league collected half of Peterson’s forfeited earnings, prorated over a 17-week basis, but held off on the remaining three-game fine pending the NFLPA’s petition to federal court that started the case that continued Monday in front of 8th U.S. Circuit judges James Loken, Diana Murphy and Steven Colloton.

Because Peterson’s base salary last year was $11.75 million, the money left to argue over is a little more than $2 million.

The injuries to Peterson’s 4-year-old boy took place in May 2014, when the personal conduct policy called for a maximum first-time suspension of two games. After the public furor over video of Rice hitting his now-wife in an elevator, Goodell announced a minimum six-game ban that August, but the union has steadfastly disputed the fairness of applying that to Peterson.