Money managers are turning on stocks that have delivered the best returns during the bull market: small caps.

Large speculators such as hedge funds are betting $2.8bn this month that the Russell 2000 (RTY) Index will fall. Thatâ??s the most since 2012 and the highest versus average levels since 2004, according to data compiled by Bloomberg and Bank of America Corp. The about-face from a year of bullish wagers coincides with lackluster performance. The gauge of the smallest companies stands 7.1 percent below its 2014 high, trailing the recovery that has put the Standard & Poorâ??s 500 Index within 1.5 percent of a record.