caught short (?.)

• ad-lib
• astonished
• caught napping
• caught off balance
• extemporaneous
• extemporized
• haphazard
• hasty
• impromptu
• improvised
• makeshift
• precipitate
• rough-and-ready
• snap
• struck with surprise
• surprised
• taken aback
• taken by surprise
• taken unawares
• tripped up
• unarranged
• unbegun
• unconcocted
• uncontrived
• undeliberated
• undevised
• unhatched
• unmade
• unmanufactured
• unorganized
• unplanned
• unpremeditated
• unprepared
• unprimed
• unready
• unstudied