をついた

hit; put against

→ を
phrase Rare #34,211
hit; put against The meaning depends on the noun before を. In 不意をついた, it means “caught someone off guard”; in ポイントをついた, “hit the key point”; and with body parts such as 肘 or ひざ, “put one’s elbow or knee down.”
JA: 彼の質問は問題の核心をついた。
EN: His question hit the heart of the issue.

我々は敵の不意をついた

We caught the enemy off guard.

トム転んでをついた

Tom fell and landed on his elbow.

そのニュースは彼の不意をついた

The news caught him off guard.

彼はがっくりとなりひざをついた

He collapsed and fell to his knees.

ポイントをついた

You hit the nail on the head.

— ザ・マン・フロム・アース (2007)