An inning is a defined segment of play in baseball and related bat and ball sports in which one team has an opportunity to bat and score while the opposing team fields, after which the teams change roles. The term is most strongly associated with baseball, where a standard regulation game consists of nine innings, subject to competition rules and possible extra innings.
Each inning is divided into a top half and a bottom half, giving each team an opportunity to bat. A team's half inning normally ends after three outs, although the precise circumstances can also involve the end of the inning when the batting team takes a lead that makes further play unnecessary in the bottom half. An inning is therefore fundamentally different from a fixed time period because it is controlled primarily by outs and game state rather than by a running clock.
The word inning is historically derived from the older English concept of taking one's turn or coming in, and its sporting use developed alongside the evolution of bat and ball games. Early forms of cricket and baseball terminology shared some concepts involving turns and opportunities to bat, although the structures diverged substantially. In modern baseball, the inning became a central organising unit because it guarantees that both teams receive an opportunity to bat and field in a defined sequence.
This creates symmetry in the contest and allows the score to be updated through repeated cycles. Cricket uses the related term innings, which has a different structure and can involve an individual batter's participation as well as a team's entire batting opportunity. The distinction between inning and innings is therefore important when comparing baseball and cricket.
A baseball inning is divided into two halves. The visiting team normally bats in the top half while the home team fields, and the home team bats in the bottom half while the visiting team fields. Each half inning continues until the batting team records three outs, although the bottom half may not be completed if the home team is already ahead when the visiting team has completed its ninth inning.
Outs can occur through several mechanisms, including strikeouts, force plays, tag plays, catches and other rule defined events. The inning therefore progresses through discrete changes of possession rather than a continuous clock. This structure gives baseball its distinctive rhythm and allows pitchers, batters and fielders to reset tactically after each half inning.
An inning is closely connected to baseball strategy because each team alternates between offensive and defensive roles. Batting teams attempt to score runs while managing outs, baserunners and the order of hitters, while fielding teams attempt to prevent scoring and record outs. The limited number of outs creates a resource that teams must manage carefully.
A batter who reaches base without making an out can extend the team's opportunity to score, while three outs terminate the half inning regardless of how much real time has elapsed. Pitching changes, defensive alignments, pinch hitters and strategic substitutions can all be influenced by the inning, score and number of outs. The same score can therefore represent very different tactical situations depending on which inning is being played and how many outs have been recorded.
The distinction between an inning and a period is especially important. A period is normally defined by time, whereas an inning is defined by opportunities and outs. A baseball inning can be extremely short if three outs occur quickly or considerably longer if many batters reach base before the third out. There is therefore no fixed number of minutes in an inning. Weather delays, pitching changes, mound visits and other interruptions can extend elapsed time without changing the fundamental structure. Because innings are not clock based, late game strategy can involve concepts such as preserving a lead, managing bullpen resources and maximising scoring opportunities within the remaining innings.
The term inning is also related to the statistical structure of baseball. Pitching statistics, batting statistics and team scoring can be analysed by inning, allowing analysts to identify patterns such as early scoring, late inning performance or defensive vulnerability. A pitcher's workload can be evaluated by innings pitched, while a team's offensive production can be measured by runs scored in individual innings. The inning also determines the context of many tactical decisions. A sacrifice play, pitching change or intentional walk can have different implications depending on the score, outs and inning. Statistical models therefore frequently include inning information because the same action can carry different strategic value at different points in the game.
Extra innings are used in baseball when the score is tied after regulation innings and the competition rules require a winner. The precise extra inning procedures can vary between professional, amateur and international competitions. Some modern formats introduce a runner on second base at the start of an extra inning to increase the likelihood of a decisive result, while historical and other formats may begin with bases empty.
The existence of extra innings illustrates that an inning is not necessarily limited to the standard regulation structure. It remains the same type of competitive unit even when the game extends beyond its normal length. The rules governing extra innings are therefore essential when interpreting records and comparing competitions from different periods.
An inning is best understood as a turn based competitive unit in which the batting and fielding roles are exchanged according to a prescribed sequence. It is not simply another word for a period, quarter, half or round because its boundaries are determined by outs and batting opportunities rather than a fixed clock. In baseball, innings organise the complete game into repeated offensive and defensive cycles and provide the basic framework for strategy, scoring and statistics. Cricket uses the related concept of an innings but structures it differently, so terminology should not be transferred mechanically between the two sports. Understanding the inning requires recognising its connection with turns, outs, alternating roles and the progression of the score.
