MINNEAPOLIS — Just as a fourth-quarter turnover can swing the momentum of a game, NFL players got a big gain at a key point in their labor fight with the league.

Writing that the NFL enhanced “long-term interests at the expense of its present obligations,” U.S. District Judge David Doty overturned a special master’s ruling and backed the NFL Players Association’s claim that the league illegally secured a potential $4 billion revenue stream for 2011 to wield against the union as lockout protection.

NFL lawyers have argued that sound business judgment was used in the last round of television contracts to maximize money for owners and players to share, but Doty disagreed.

The union’s contention is that the league left money on the table for broadcast rights to the last two seasons in those negotiations with the networks to create a war chest for this year.

The current collective bargaining agreement expires at midnight Thursday night, and a lockout could come next.

The league and the NFL Players Association are scheduled to resume negotiations overseen by a federal mediator today in Washington. About 25 miles west from there, team owners will begin gathering at a hotel in Chantilly, Va., to get an update on where the bargaining stands — and decide what they should do.

Doty criticized special master Stephen Burbank for legal errors and erroneously concluding earlier this month that the NFL can act like a self-interested conglomerate when in fact it is bound by legal agreements to make deals that benefit both owners and players.

“The record shows that the NFL undertook contract renegotiations to advance its own interests and harm the interests of the players,” wrote the judge, who has overseen NFL labor issues since he presided over a 1993 settlement that cleared the way for the current free agency system.

The union had asked that the TV money be placed in escrow until the end of any lockout, so the owners can’t use it as a safety net, thus equalizing the risk level for both sides during a protracted work stoppage. Doty will preside over a hearing, yet to be scheduled, to determine potential damages for the players as well as an injunction involving the TV contracts.

NFL spokesman Greg Aiello downplayed the significance of the ruling, saying the 32 teams were “prepared for any contingency.”

The union accused the NFL of failing to secure the maximum revenue possible when it restructured broadcast contracts in 2009 and 2010, claiming the deals were designed to guarantee owners enough money to survive a lockout. The union argued this violated that 1993 agreement between the sides that orders the NFL to make good-faith efforts to maximize revenue for players.