I have taught Small Business Management, Marketing, and Entrepreneurship for several years at 2 different colleges so I would like to offer up a few nuggets of advice I believe may help you. Before taking a critical risk such as this, I would formulate some critical questions, research the answers, and attempt to be as objectively honest as possible. Here are some examples:
1) There are many competitors in the Sportswear market and they all have something unique to offer the customer. Ask yourself: What makes your product unique and different? Is this uniqueness enough to overcome the established business practices of your competitors?
2) Do you have a sound product delivery strategy? Are you placing products in retail stores? Mail order delivery? Opening your own store front? All of the above? Do the math. Make sure the costs of delivery/retailing are factored in to allow for profitability.
Above all, put together a business plan that is realistic. It is often easy to be overly optimistic and project sales predictions on the basis of a "great idea" but reality can often be very different. Taking the time to do thorough target market research can do a lot to reveal whether your product is truly going to be something that people want to buy.
Hope this helps and best of luck to you!