Remove all support and assistance from, usually suddenly. For example, Stopping his allowance pulled the rug out from under him, forcing him to look for a job. This metaphoric term alludes to pulling on a rug a person is standing on so that he or she falls. [Mid-1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.