運動会 (うんどうかい ) Sports Day
The explanation for this word sounded familiar. Sure enough after a little googling, I found that it is equivalent in the USA to Field Day. Apparently Sports Day if the British term. Down the rabbit hole I went… and started to wonder if the idiom using field day is translated using this word in Japanese or does it have another phrase.
e.g . When the boss left his phone unlocked at the office, the workers had a field day looking through his private photos.