Wiktionary
fall back on
vb. (context transitive English) To turn to as a substitute.
Usage examples of "fall back on".
It was so warm, and he was so cold that he shivered when she covered him up, and then, with the ease of old habit, he let his arm fall back on the pillow and she eased into his side and laid her head on his chest.
He knew that in a short while the Invaders would discontinue their attempts to make an immediate capture, would conclude that he had found shelter, and would fall back on an inescapable slow search that could not help but root him out sooner or later soon, if he stayed this near the headquarters that would be the focal point for the expanding boxes of a square search.