Individual investors are backing a new underdog, Avaya Holdings pumping up the software company’s downtrodden stock by about 200% over the past month and confounding Wall Street professionals. Avaya’s fans include day traders who congregate on Reddit and Twitter forums, and a 35-year-old software entrepreneur who has snapped up a 15% stake. They are facing off against a group of large fund managers such as Apollo Global Management and Ares Management that could benefit if the company seeks bankruptcy-court protection.

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