Shares of Unisys (NYSE: UIS), Organogenesis Holdings (NASDAQ: ORGO), and Motorcar Parts of America (NASDAQ: MPAA) fell today as all three stocks were removed from the S&P SmallCap 600 index as part of its quarterly rebalancing. Unisys closed the day down 14.1%, Organogenesis lost 18.5%, and Motorcar Parts of America gave up 12.2%. There are several reasons stocks fall when they're removed from a major index like the S&P SmallCap 600.