set back on one's heels

set back on one's heels or knock back on one's heels  {v. phr.},  {informal}

To give an unpleasant surprise; upset suddenly; stop or turn back (someone's) progress.

Jack brags too much and it set him back on his heels when the coach told him he wasn't as good a player as he thought he was.

Jean was doing very well in school until sickness knocked her back on her heels.

Compare: KNOCK FOR A LOOP, THROW FOR A LOSS.