The addition to the S&P will have attracted more non index funds/institutions to build long positions. This makes it really tough for large shorts to cover with a mid cap. . Once they take their hit, say at end of Q1 or whatever, they still eventually have to cover by buys, options or otherwise. It is reasonable to expect we exit March 31 with a significant short position. The problem for shorts is that growth of earnings will rapidly keep things strong over time, reducing the chances of a major pullback other than as reflected across the market. Stocks that outpace the market however are very poor shorting candidates. Do I hear a train coming ?