Rule 10a-1(redirected from Rule 10a1)
An SEC rule that formerly prohibited a short sale except on a plus tick or a zero plus tick. That is, Rule 10a-1 disallowed short sales at a price below the price at which the security traded most recently. This rule was intended to prevent short sellers from artificially deflating a security's price so that it harmed other investors. It was also called the uptick rule. It was replaced by Regulation SHO in 2007. Some have argued for its reintroduction.
A 1939 SEC rule that prohibits the short sale of a security at or below the last price at which that security was traded, unless the last price was higher than the previous different price. Rule 10a-1 was instituted to keep short sellers from battering down the price of a stock.