The lawyer's apparently innocent question was designed to catch the witness off (his) guard.

律师看似不经意的问题是为了使证人措手不及。

《牛津词典》

He had a way of throwing Helen off guard with his charm when she least expected it.

他有办法用他的魅力让海伦在最意想不到的时候失去戒备。

《柯林斯英汉双解大词典》

In the end a guard arrived in his car, and the lion just got off our car and started smelling the guard's hand as if nothing was the matter.

最终，一个警卫开车来了，狮子就从我们车上下来，开始嗅着警卫的手，就好像什么都没发生似的。

youdao

Just as it looked as though his cards were played out, the wily Mr Chaudhry has caught his opponents off guard by tendering his resignation.

ECONOMIST: Fiji

Gerrard was allowed time and space with the ball in midfield and he used it to telling effect as he slid a ball through to Torres, who took a lovely first touch and held off Gary Caldwell before catching Al-Habsi off guard by taking his shot early to find the bottom corner.

BBC: Fernando Torres puts Liverpool ahead at Wigan

But midway through the interview, he was caught off guard when his interviewer asked him for his Klout score.

FORBES: Do You Have Klout? Employers Want To Know