catch someone off guard

The surprise birthday party really caught me off guard because I had no idea what was happening.

サプライズの誕生日パーティーは何が起こっているのか全く知らなかったので、本当に私を驚かせた。

The unexpected question from the reporter caught the politician off guard during the press conference.

記者会見中、記者の予想外の質問は政治家を不意を打たれて困らせました。