<P> An inning in baseball, softball, and similar games is the basic unit of play, consisting of two halves or frames, the "top" (first half) and the "bottom" (second half). In each half, one team bats until three outs are made, with the other team playing defense . A full game typically is scheduled for nine innings, although this may be shortened due to weather or extended if the score is tied at the end of the scheduled innings . </P> <P> Each half - inning formally starts when the umpire calls "Play" or "Play ball". A full inning consists of six outs, three for each team; and, in Major League Baseball and most other adult leagues, a regulation game consists of nine innings . The visiting team bats in the first half - inning, 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 the bottom of the inning, and the break between halves of an inning is the middle of the inning . If the home team is leading in the middle of the final scheduled inning, or scores to take the lead in the bottom of the final scheduled inning, the game immediately ends in a home victory . </P> <P> In most leagues, if the score is tied after the final scheduled inning, 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). For the 2011 and 2012 NPB season, a game also ended in a tie if a regular - season game has reached its 3 - hour, 30 - minute time limit and both teams are tied . 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 ice hockey where the team (either home or away) scoring first in overtime automatically wins . </P>

When does a new inning start in baseball