An inning in baseball or softball consists of two halves, where a single half is sometimes called a frame. In each half, one team bats until three outs are made, with the other team playing defense. Each half-inning formally starts when the umpire calls "Play". A full inning consists of six outs, three for each team; and a regulation game consists of nine innings. The visiting team always bats first in each inning, and the visitors' turn at bat is called the top of the inning, derived from the position of the visiting team at the top line of a baseball line score. The home team's half of an inning is also called the bottom of the inning, and the break between halves of an inning is called the middle of the inning. If the home team is leading in the middle of the ninth inning, or scores to take the lead in the bottom of the ninth inning, the game immediately ends in a home victory.
If the score is tied after nine innings, the game goes into extra innings until an inning ends with one team ahead of the other. In Japanese baseball, however, games end if tied after 12 innings (or, in postseason play in Nippon Professional Baseball, 15 innings). As in the case of the ninth inning, a home team which scores to take a lead in any extra inning automatically wins, and the inning (and the game) is considered complete at that moment regardless of the number of outs. This is commonly referred to as a "walk-off" situation, since the last play results in the teams walking off the field because the game is over. However, road teams can't earn a "walk-off" victory by scoring the go-ahead run in extra innings, unlike in American football and ice hockey where the team (either home or away) scoring first in overtime automatically wins.
A baseball game can be shorter than nine innings if it is interrupted by rain (or other bad weather). Such a game, called a rain out, it often preceded by a rain delay, a pause in the game during which the umpires will try to determine if the weather will eventually let up and allow the game to continue. If so, the game will simply be delayed until the rain stops, and then play will resume. If not, the umpires will announce a rain out and play will be suspended for the day. The game may have to be replayed in its entirely at a later date, but under certain circumstances, a game shortened because of rain can count as an official game, and the team that was ahead at the time the game was called will be awarded the win. See the article on rainout (baseball) for further details.
Ending a half-inning is referred to as "retiring the side". A half-inning in which all batters are put out without taking a base is referred to as a "one-two-three inning". The number of innings a pitcher is in a game is measured by the innings pitched statistic.
In US English, baseball terminology is sometimes found in non-sports usage in a tense situation: "it's the bottom of the ninth [inning]" (sometimes adding, "with two outs"), meaning "there isn't much time to turn things around here".
Professional baseball games (both major and minor leagues) as well as college baseball games last nine innings. High school games and College softball last seven innings and Little League uses six inning games.
- Baseball Explained by Phillip Mahony, McFarland Books, 2014. See www.baseballexplained.com