While the concept of the rule has been around since 1930s, the current version went into effect in 2010 after the global financial crisis. The SSR rule restricts short sellers from piling into a stock whose shares have dropped by 10%. Once triggered, it becomes impossible for you to short the stock.
Short Sale Restricted. SEC rule that kicks in after a stock has decreased 10% from previous day's closing price. It begins when stock reaches 10% drop and extends into the next trading day. It slows shorting. Shorts can only short during a price uptick when it's in force. Some folks say it's ineffective. Research on google.
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