The Kentucky-based private-equity firm founder and manager John Stewart, whose aggressive spending and outspoken attitude have made a big splash in the global bloodstock and racing worlds since he entered the Thoroughbred business from scratch a little more than a year ago, is being sued in a New York court by an investment firm that provided initial funding for Stewart's MiddleGround Capital. That plaintiff, Archean Capital Partners, is now alleging that Stewart and other MiddleGround defendants are acting in "bad faith" for purportedly falling behind and refusing to pay $22...