Dominic Ball, an analyst at Rothschild & Co Redburn, is the only analyst with a sell rating on Fiserv Inc. On Wednesday, the fintech firm slashed its full-year earnings forecast and the stock dropped 44%. It's down nearly 70% over the last year. Ball says there are issues with the company's Clover point-of-sale system. He speaks on "Bloomberg Open Interest." (Source: Bloomberg)