New Delhi, Aug. 22 -- Tennis apparel sponsorship is a big business. It is also one that, among the top players, is dominated by a small group of industry titans.

Brands like Nike, Adidas and Asics provide the outfits for most of the top 100, with their recognizable logos splashed across the shirts and skirts of Grand Slam favorites.

But if one looks beyond that upper echelon and into the U.S. Open's qualifying tournament - where lower-ranked players compete for spots in the main draw - there's a world of local startups and small clothing businesses making their way into the booming tennis business.

For many players in the qualifying tournament, their apparel sponsors are companies local to their home country. These companies often spec...