{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.
See: SET BACK ON ONE'S HEELS.