A different/new ball game - Idioms by The Free Dictionary
a different/new ball game
a (whole) new ballgame
A situation that is completely different from what one is used to or expecting. Living away from home is a whole new ballgame for most young adults. I used to babysit, but having a child of my own is a new ballgame.
a (whole) different/new ˈball game (informal) a completely different kind of situation: They used to go out every night, but now they’ve got a baby it’s a whole new ball game.