Most of us have articles of clothing from either Nike or Under Armour. They are industry giants when it comes to sportswear and team apparel. This is an ongoing case between the two over the "I Will" mark. Under Armour claims ownership of the mark, and Nike claims that it has been using the noun-verb combination since at least 1995. The dispute follows the trajectory of typical trademark lawsuits: Under Armour filed for trademark infringement. Nike counterclaimed for a declaratory judgment of invalidity.
In trademark infringement suits, the defendant often counterclaims for a declaratory judgment of invalidity. This basically "ups the ante," because there are more potential consequences: namely that the mark may be invalidated. So a plaintiff who is unsure of his or her claim might think twice about continuing the suit, if the defendant seeks to invalidate the trademark.