1
general::
1. Give ground, retreat, as in The troops fell back before the relentless enemy assault, or He stuck to his argument, refusing to fall back. [c. 1600] 2. Recede, as in The waves fell back from the shore. [c. 1800]
American Heritage Idioms
2
general::
Phrase(s): fall back
to move back from something; to retreat from something. • The gang members fell back, and I took that opportunity to get away. • The troops fell back to regroup.
McGrawhill's American Idioms And Phrasal Verbs