Shares of Under Armour Inc. UAA, -0.36% slumped 0.8% in premarket trading Monday, after S&P Dow Jones Indices said it was booting the athletic apparel and gear maker from the S&P 500 SPX, +0.95%. The company, and IPG Photonics Corp. IPGP, +0.23%, are moving down from the large capitalization index to the S&P MidCap 400 MID, +1.74%, S&P Dow Jones Indices said late Friday, while Trinity Industries Inc. TRN, +0.34% and Yelp Inc. YELP, +0.26% are dropping to the S&P SmallCap 600 SML, +1.10%. Shares of Keurig Dr Pepper Inc. KDP, -0.79% rallied 8.1% and ON Semiconductor Corp. ON, -0.80% climbed 7.2%, as the companies are replacing Under Armour and IPG Photonics in the S&P 500.