What: Harley-Davidson (NYSE:HOG), one of the most storied and recognizable brands in America, saw its stock plunge more than 15% on Tuesday morning after it reported a disappointing third quarter, due to increased competition and foreign exchange remaining a headwind.

Harley-Davidson Chief Executive Matt Levatich put it bluntly: "The third quarter did not unfold as we expected." 

So what: Harley-Davidson's worldwide retail sales declined 1.4% to 72,178 units, which was dragged down by a 2.5% decline in U.S. retail sales. Furthermore, revenue from motorcycles and related products rose a meager 0.9% to $1.14 billion, which fell short of analyst estimates of $1.21 billion. While revenue did post a 0.9% gain over last year's third quarter, it was offset by a 5.2% unfavorable currency exchange, which is a headwind likely to persist at least through the remainder of 2015. Earnings per share checked in flat year over year at $0.69, but that also fell far short of the $0.78 estimated by analysts.

Perhaps most concerning was Harley-Davidson's 3.9 percentage-point decline in U.S. new 601+ CC (heavyweight motorcycle) market share, or 390 basis points, from 56.3% during last year's third quarter to 52.4% currently. Year-to-date market share tells a similar story, as Harley-Davidson's retail market share of the new 601+ CC segment sits right at 50%, compared to 53.7% through the same time period in 2014.

Now what: A challenging third quarter forced management to reduce its worldwide shipment projection by 11,000 to 265,000-270,000 -- that's down about 2% compared to 2014, and down from the previously expected 276,000-281,000 range. Furthermore, in part due to the disappointing results, Harley-Davidson expects to incur between $30 million and $35 million in fourth-quarter expenses due to looming layoffs and related costs. 

Going forward, Harley-Davidson plans to increase product and brand awareness through increased advertising, grow new ridership in the U.S. market through its rider training programs, and open between 150 and 200 dealerships globally by 2020 to try to stoke growth for investors.