The Under Armour brand was born on the gridiron as former University of Maryland football player Kevin Plank set out to create the world's best performance T-shirt for athletes. But it was UA's decision to go into business with the country's most popular and powerful sports league -- the NFL -- that helped propel the upstart athletic company to the next level.

Since 2009, UA has sponsored the NFL Scouting Combine: an invitation-only event where 300 to 350 of the country's top draft prospects run the 40-yard dash, lift weights and complete other athletic drills. All players must wear UA shirts, shorts and socks. That kind of exposure in front of the next generation of NFL stars, and millions of TV viewers, helped put UA into the same league as Nike , Adidas and Reebok. UA is now part of an event that could become as big a marketing/media play as the NFL draft.

 This year for the first time, Under Armour added a retail component to its NFL Combine sponsorship. UA and NFL created a NFL Scouting Combine brand logo, which means UA was able to sell Combine gear with NFL trademarks on its website. Meanwhile, UA got its own online store selling UA-NFL Combine Gear at NFLShop.com. 

The exposure of the NFL Combine deal helps UA's brand in a couple of ways. It enables the brand to show off its base-layer products that are worn underneath the NFL uniforms -- but not visible on TV. Also, UA gets to associate itself with future stars in the period between when they leaving college and join the NFL Players Association. The better a player performs at the Combine, the more likely UA is to sign him as endorser.  

The NFL Shield "just gives you great credibility," said Matthew Mirchin, UA's senior VP-global brand and sports marketing. "The Combine gave us a broader platform to tell our story and reach more football players -- whether they be guys going to the Combine, guys already in the NFL or just athletes around the world."

UA has posted 10 straight quarters of 20%-plus revenue growth and is on track to reach $2 billion in sales for the first time. Mr. Mirchin ticked off the big new products highlighted at the event, including: the E39 electronic compression shirt; core short; Highlight cleats; and the Warp collection of shirts, shorts and gloves. As sponsor, UA sets up a players' lounge with TVs and pool tables at a hotel in Indianapolis.

Company executives mingle with the young players and get feedback on style, color and design. These informed consumers tell teammates about UA.

"You can't get a better endorsement than an athlete who wears your products—because they like your products," Mr. Mirchin said.