1
general::
Phrase(s): sit back
to push oneself back in one’s seat; to lean against the back of one’s seat. • Please sit back. I can’t see around you. • I sat back and made myself comfortable, assuming that the movie would bore me to sleep.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
1. Relax, as in Now that the work's finished, we can just sit back. 2. Refrain from interfering or taking part, as in Mom and Dad just sat back and watched Meg try to decide whether or not she should tell on her friends. [Mid-1900s] Also see SIT BY.
American Heritage Idioms