2016 Softball Rulebook
Section 2, Definitions:
An INNING is that portion of a game within which the teams alternate on offense and defense and in which there are three put outs for each team.
It will be held that an inning starts the moment the third out is made completing the preceding inning.
(Minor League Only - A five-run limit is to be imposed which would complete the half inning.)
When three offensive players are legally put out, that team takes the field and the opposing team becomes the offensive team (side retired).
(Minor League: The side is retired when three offensive players are legally put out, called out by an umpire, or when all players have batted one time in the half-inning or when the offensive team scores five (5) runs).
(OPTION: The local league Board of Directors may suspend the five-run rule in the last half-inning for either team)....