catch sb. on the wrong foot catch sb. with his pants down
Related Translations:
措手不及: (事情来得太快, 出乎意外, 来不及应付) be taken by surprise; be caught unawares [unprepared]; be too late to do anything about it; be too surprised to defend oneself; could make no adequate defense; could
我军行动神速致使敌军措手不及狼狈周章: our lightning speed knocked the enemy completely off balance and struck fear into its heart