BSN Sports is the largest manufacturer of custom sporting apparel for high schools in the United States. BSN is the largest manufacturer of custom sporting apparel for high schools in the United States. If you've ever seen a high school sell T-shirts with their logo on them, or you've seem a high school with really nice uniforms, there is a very high chance that BSN Sports produced them. They product all sorts of apparel and accessories, from T-shirts to sweatpants to football jerseys to water bottles. They can even take footballs and engrave them with a laser.