NOBULL, which defines itself as “a brand for people who train hard and don’t believe in excuses,” has received an unspecified investment from Exeter Capital, a new private equity firm in Boston, to help it to grow and expand its product line. The company, which recently took over the sponsorship of the CrossFit Games from Reebok, was founded in 2015 by two Reebok veterans, Marcus Wilson and Michael Schaeffer, as a direct-to-consumer brand of apparel, footwear and accessories. In addition to its web store, it operates three physical stores in the U.S. It focuses on training, but it has recently added items for cycling, running and trail running.