Showing much more vigor than its many naysayers imagined, Amazon.com (NASDAQ:AMZN) flexed its muscles again today and launched a sporting goods store. Partnering with established merchants, Amazon offers "hundreds of thousands" of products covering 3,000 brand names and 50 sports, making the site a must-visit for sports fans.

Partners include Sports "R" Us, a new venture launched by Toys "R" Us (NYSE:TOY), and Sportman's Guide (NASDAQ:SGDE) -- a company whose steady rise has been covered by The Motley Fool's Matt Richey and highlighted early in Motley Fool Hidden Gems.

Since setting out with books in 1995, Amazon has launched several new product categories every year, starting with music and DVDs, before branching into electronics, kitchenware, toys, apparel -- you name it -- and fighting skeptics along the way.

Any doubt raised over Amazon's sporting goods initiative will be misplaced. The market is highly fragmented, with the top five retailers commanding just 11% of sales in the giant market, making the situation ripe for new entrants and new leaders.

Amazon's top competitors (who don't appear to be partners) include The Sports Authority (NYSE:TSA), with $1.4 billion in annual sales, Dick's Sporting Goods (NYSE:DKS), with $1.2 billion in revenue (Dick's is another company the Fool has analyzed), Big Five (NASDAQ:BGFV), Galyan's (NASDAQ:GLYN), and eBay (NASDAQ:EBAY).

To get the ball rolling, Amazon is offering $10 in general credit when $50 is spent in the sporting goods store. Spending 50 bucks probably won't be a problem for sports enthusiasts.

David Gardner has made a career of defying the doubters. Little surprise David made Amazon his top pick in Motley Fool Stock Advisor last October at roughly one-third of today's prices.