If someone is struck down, they die suddenly or start to suffer from a serious illness.

It's a tragedy that these young people were struck down in their prime. 这些年轻人英年早逝真是令人痛心。

He was struck down by polio when he was a teenager. 他十几岁时患上了脊髓灰质炎。

to rule that a law is illegal and should not be obeyed

The courts struck down local segregation laws because they violated the federal constitution. 法庭裁决当地的隔离法非法，因为该隔离法违反宪法。