The uptick rule refers to a trading restriction that disallowed short selling of securities except on an uptick. For the rule to be satisfied, the short must be either at a price above the last traded price of the security, or at the last traded price if that price was higher than the price in the previous trade. The rule went into effect in 1938 and was removed when Rule 201 Regulation SHO became effective in 2007. A paper from the New England Complex Systems Institute claims that they have found evidence that suggests the 2008 financial crisis was triggered by a "Bear Raid" market manipulation by short sellers against Citigroup late in 2007. The uptick rule was repealed in in July, 2007, and the alleged bear raid took place in November, 2007.



