catch someone napping 20385

catch someone napping and catch someone off balance; catch someone up short
to come upon someone who is unprepared; to surprise someone. (See also asleep at the switch.) The enemy soldiers caught our army napping. The thieves caught the security guard napping. I didn't expect you so soon. You caught me off balance. The teacher asked a trick question and caught me up short. The robbers caught Ann off balance and stole her purse