set you back on your heels
set (one) back on (one's) heels
To put one into a state of surprise, unease, or bemusement, especially such that it affects their ability to perform or function. The sudden arrest of one of our teammates last night certainly set us back on our heels, and we weren't able to play to the best of our abilities this morning. The tragedy set the entire community back on their heels.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
set you back on your heelsor
rock you back on your heels
If something sets you back on your heels or rocks you back on your heels, it surprises or shocks you. Something very odd occurred, and it set me back on my heels. Ireland started well, only to be rocked back on their heels by the first error just 10 minutes into the match.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012