An inning, or innings, is a fixed-length segment of a game in any of a variety of sports – most notably cricket and baseball during which one team attempts to score while the other team attempts to prevent the first from scoring. In cricket, the term innings is both singular and plural and is always spelled and pronounced with the terminal "s." In baseball, the singular form is inning and only the plural takes an "s."
In many other sports, the length of the game is dictated by a clock and teams swap offensive and defensive roles dynamically by taking possession of a ball or similar item. In baseball and cricket, however, one team, said to be "batting," attempts to score "runs"—see run (baseball) and run (cricket)—while the other team, said to be "fielding," attempts to prevent the scoring of runs and get members of the batting team out. The teams switch places after the fielding team has succeeded in getting a fixed number of players out, making a clock unnecessary.
In cricket, the term innings is also used to refer to the play of one particular player (Smith had a poor innings, scoring only 12). By extension, this term can be used in British English for almost any activity which takes a period of time (The Liberal government had a good innings, but finally lost office in 1972, or You've had a fair innings, now it's my turn, meaning "you have spoken for long enough, now let me speak"). It is also used in reference to someone who has died at a reasonably old age or lived a rich and rewarding life (Ah, well. John was 83. At least he had a good innings). The baseball-derived parallel to this in American English is the term at bat.
According to the Oxford English Dictionary, the term innings has been used in reference to cricket since at least 1735. As cricket was a mature, highly organized sport in the 1600s in England, the term's origin could well precede this first recorded usage. The word inning meaning 'a gathering in' is first recorded in 1522, and could be related.
In First-class cricket and Test cricket, each side has two innings. In one-day cricket and other abbreviated forms of the game, an innings lasts only for a set period or for a certain number of overs (typically 50). Note that "an innings" can mean either a particular side's innings (Sri Lanka made 464 in the third innings (of the game)) or that of both sides (England had the better of the first innings, outscoring Australia by 104), the difference being understood by context.
An individual innings usually lasts until the batsman is given out, or until the end of the team innings. Although batsmen bat together in pairs, this combination is never called an innings: it is a partnership or a stand.
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. 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.
In US English, baseball terminology is sometimes found in non-sports usage in a tense situation: "it's the bottom of the ninth with the home team behind," 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 last seven innings and Little League uses six inning games.