Which rule states that the last change in a stock price must be positive for a short sale to occur?

The Uptick Rule is a regulation that requires the last transaction price of a security to be higher than the previous price before a short sale can be executed. This means that a trader can only sell short if the most recent trade has moved up in price, indicating that there is some momentum or positive sentiment in the stock's price movement. The purpose of this rule is to prevent excessive downward pressure on a stock's price during periods of heightened volatility, which could occur if many investors were allowed to short a stock regardless of its previous price changes.

This rule aims to create a more stable market environment by curbing potential manipulation and allowing investors to better assess the true value of the stocks they are trading. The Uptick Rule helps maintain market integrity by ensuring that short selling is done in a manner that does not exacerbate falling prices and encourages responsible trading practices.