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.
whole new ballgame, a
A completely altered situation, as in It will take a year to reassign the staff, and by then some will have quit and we'll have a whole new ballgame . This expression comes from baseball, where it signifies a complete turn of events, as when the team that was ahead falls behind. [Colloquial; 1960s]