be caught unprepared “措手不及

“措手不及”，汉语成语，指的是事情突然出意外，一时无法对付。可以翻译为“be caught unprepared，be caught on the wrong foot或be thrown off one's guard”等。

例句：

这一举动为的是让对手措手不及。

It was an attempt to wrong-foot the opposition.

马林斯突然改变话题，这让我措手不及。

Mullins knocked me off-balance with his abrupt change of subject.