One ball is subtracted from your inventory per hole.
In Career, sets of 3 holes will use 3 balls, and special stages with 6 holes will use 6 .
In Match mode, one ball will be used, even if the game goes to a tiebreaker.
In Tournament Mode, One ball will be used per hole.
In Clan League Mode, one ball will be used per hole completed.

You may go into a game with less than the required number of balls left, and when you run out you will go back to the default free White ball.