这个英语表达指“趁他人毫无防备时做某事，而使其感到措手不及”。在这里，“catch”的意思是“撞见、发现”，强调动作的偶然性；而短语“off guard”则用来形容人“毫无警惕心的，措手不及”的状态。

例句

The teacher caught everyone off guard when she suddenly announced that there would be a test.

老师突然通知大家要做课堂小测验，这可打了所有人个措手不及。

The government's decision to raise the interest rate caught everyone off guard - nobody expected it.

政府提升利率的决定令所有人猝不及防 — 没有人预料到这件事。

The news about the couple's engagement caught everyone off guard as everyone thought they had split up.

这对情侣的订婚消息让所有人感到措手不及，这是因为人们都以为他们已经分手了。