From Longman Dictionary of Contemporary Englisha whole new ball gamea whole new ball gameDIFFERENTa situation that is very different from the one you are used to I used to be a teacher, so working in an office is a whole new ball game. → ball game
Examples from the Corpus
a whole new ball game• I used to be a teacher, so working in an office is a whole new ball game.• Although not my cup of tea, I must admit Manchester United is a whole new ball game.• So obviously if he's hidden this one, he's playing a whole new ball game.• Read in studio Still to come on Central News, it's a whole new ball game. 