off guard

Not vigilant; unprepared; inattentive. / Unexpectedly or by surprise.

Japanese Meaning

油断している / 警戒心がない / 用心深さを失っている / 不意に、予期せぬ形で（行動する・起こる）

He was caught off guard by the sudden question during the interview.

彼は面接中の突然の質問に不意を突かれた。

Sense（1）

Not vigilant; unprepared; inattentive.

His sudden appearance at the office caught her completely off guard.

Sense（2）

Unexpectedly or by surprise.