NWSL players can no longer freely sign shoe sponsorships: the league wants a cut of the money, and it's turning into a showdown between brands, players and the NWSL.

Several NWSL players have flashed a middle finger (or two) to referees in recent years, but Michelle Cooper's form of defiance toward league authority this year may not look very controversial at first glance: her cleats. She celebrated her game-winning goal in the Kansas City Current's thrilling 3-2 win over the North Carolina Courage on Saturday by kneeling and removing her right boot to hold it up and show it off to the crowd. It was not the first time this summer that Cooper made a point to highlight her New Balance boots -- and her reasoning has everything to do with a monetary battle off the field.

The NWSL now requires brands to pay not just the players, but the league, for the right to have the brand's boot logo shown on the field. Cooper's cleat sponsor, New Balance, has no such deal in place. Brands that don't pay up will have their products prohibited from being shown: if players wear them, the brand logos must be covered up. Players who don't oblige with covering the unsanctioned logos, like Cooper, will be fined. While a footwear policy is common in other American professional sports leagues, it is a foreign concept in global soccer.

Per the NWSL footwear policy that was implemented this year, any brand outside of league sponsor Nike must make a qualifying payment to the league, believed to be a minimum of $100,000. In addition, the brand must pay all sponsored players a minimum of $5,000 to wear that brand in official NWSL competitions. As of late August, only Adidas and Puma signed the league's agreement to join Nike as an authorized footwear provider.