If you start the next inning you have to get to three total batters faced. I'm thinking this is a bad rule change. One of the main factors for instituting the 3 batter rule was to speed up the game. So now if a reliever faces one or two batters and the inning ends, he comes back out for a batter, only to probably/possibly stop the game for a pitching change when it could've been done in between innings. You can make the change between innings if you want. It's just if you don't, the 3 batter minimum holds for the pitcher you leave in.