From Longman Dictionary of Contemporary Englishfield dayˈfield day noun 1 → have a field day2 [countable] American EnglishSE a day when students at a school have sports competitions and parents watch SYN sports day British English
Examples from the Corpus
field day• His nomination could be a field day for Democrats.• Those looking into dodgy dealings at the county jail, on the other hand, have had a field day.• Any bacteria that may be in the food will have a field day and grow.• The tabloid newspapers would have a field day. 