off base - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Wrong, relying on a mistaken premise, as in His description of the accounting system was totally off base. This metaphoric term originated in baseball, where a runner who steps off a base can be put out. [c. 1940]