not careful or prepared for sth difficult or dangerous :
The lawyer's apparently innocent question was designed to catch the witness off (his) guard .
not careful or prepared for sth difficult or dangerous :
The lawyer's apparently innocent question was designed to catch the witness off (his) guard .
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005