DraftKings Inc., Flutter Entertainment PLC and other stocks linked to the sports gambling industry tumbled on Friday after new data suggested that they may be losing ground to competing products from prediction market startups. Platforms like Kalshi and Polymarket, which have recently introduced financial contracts tied to the outcome of sports games, reported surging activity last week during the beginning of the NFL playoff season. Meanwhile, during what is typically a boom time for sportsbooks, New Yor ...