To upset someone’s plans or activities; to remove someone’s supports. The image is undeniably clear, but a more common practice, it would seem, would be the schoolboy trick of pulling a chair away from someone who is about to sit down. It is rug, however, that became part of a common turn of phrase, originating in the mid-twentieth century. Time used it in an article about labor and the economy in 1946: “Strikes, for instance, would pull the rug out from under the best of prospects.”