also: イエロー・フラッグ
noun
yellow flag (racing)
In motorsports, a yellow flag signals caution, such as an obstacle on the track.
コース上に事故があったため、イエローフラッグが振られた。
A yellow flag was waved because there was an accident on the track.
noun
In American football, a yellow flag thrown by an official indicates a penalty.
審判がイエローフラッグを投げ、反則が宣告された。
The referee threw a yellow flag and a penalty was called.