About a year-and-a-half ago, Warriors superstar Steph Curry nearly ended his relationship with Under Armour. Kevin Plank, the sports apparel company's founder and chief executive, and Patrik Frisk, its president and chief operating officer, needed to persuade Stephen Curry, the Golden State Warriors star and the company's highest-profile endorser, not to leave the brand. Mr. Plank was unhappy that Mr. Curry, whose endorsement deal pays him millions of dollars a year, would rarely wear Under Armour clothing to N.B.A. games.