set one back on 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.
set one back on one's heels
Fig. to surprise or shock someone. I'll bet that news really set her back on her heels! The bill for the repairs set me back on my heels.