Definition
to launch an unexpected attack on someone
突然襲擊；偷襲…
The sudden threat caused panic in the team as the enemy fell upon them out of nowhere.
突如其來的威脅讓團隊陷入恐慌，敵人從不知名的地方突然襲擊了他們。
The gang crept in at night and then fell upon the store in a surprise raid.
這幫人趁夜潛入，然後對商店發動了一場突襲。
The news of the volcanic eruption fell upon the residents like a bolt from the blue.
火山噴發的消息如晴天霹靂般降臨在居民身上。