General structure Baseball is played between two teams with nine players in the field from the team not batting at that point (the batting team would have one batter in play at "home plate" on the field). On a
baseball field, the game is under the authority of several umpires. There are usually four umpires in major league games; up to six (and as few as one) may officiate depending on the league and the importance of the game. There are three
bases. Numbered
counterclockwise, first, second, and third bases are cushions (sometimes informally referred to as
bags) shaped as square in Major League Baseball, or in other rulesets (including Little League, Babe Ruth, American Legion, and NFHS) which are raised a short distance above the ground. Together with
home plate, the fourth "base", they form a square with sides of called the diamond. Home plate is a pentagonal rubber slab wide. The playing field is divided into three main sections: • The infield, containing the four bases, is for general defensive purposes bounded by the foul lines and within the grass line (see figure). • The outfield is the grassed area beyond the infield grass line between the foul lines and bounded by a wall or fence. • Foul territory is the entire area outside the foul lines. The pitcher's mound is located in the center of the infield. It is an diameter mound of dirt no higher than . Near the center of the mound is the pitching rubber, a rubber slab positioned from home plate. The pitcher must have one foot on the rubber at the start of every pitch to a batter, but the pitcher may leave the mound area once the ball is released. The desired alignment of the field (home plate to second base) is
east-northeast. At the college/professional level, baseball is played in nine
innings where each team gets one turn to
bat and tries to score
runs while the other pitches and defends in the field. High school baseball plays seven innings and
Little League uses six-inning games. An inning is broken up into two halves where the away team bats in the top (first) half, and the home team bats in the bottom (second) half. In baseball, the defense always has the ball which differentiates it from most other team sports. The teams switch every time the defending team gets three players of the batting team
out. The winner is the team with the most runs after nine innings. If the home team is ahead after the top of the ninth, play does not continue into the bottom half. When this happens, an X is put on the scoreboard for the home team's score in the ninth inning. In the case of a tie, additional innings are played until one team comes out ahead at the end of an inning. If the home team takes the lead anytime during the bottom of the ninth or of any inning after that, play stops and the home team is declared the winner; this is known as a walk-off. The basic contest is always between the
pitcher for the fielding team and a
batter. The pitcher throws
pitches the ball towards home plate, where the
catcher for the fielding team waits (in a crouched stance) to receive it. Behind the catcher stands the home plate umpire. The batter stands in one of the
batter's boxes and tries to hit the ball with a bat. The pitcher must keep one foot in contact with the top or front of the pitcher's rubber—a plate located atop the pitcher's mound—during the entire pitch, so he can take only one step backward and one forward in delivering the ball. The catcher's job is to receive any pitches that the batter does not hit and to "call" the game by a series of hand movements which signal to the pitcher what pitch to throw and where. The catcher also usually signals the desired location of the ball within the strike zone and "sets up" behind the plate or holds his glove up in the desired location as a target. The catcher's role becomes more crucial depending on how the game is going, and how the pitcher responds to a given situation. Each pitch begins a new
play, which might consist of nothing more than the pitch itself. Each half-inning, the goal of the defending team is to get three members of the other team out. A player who is out must leave the field and wait for his next turn
at bat. There are many ways to get batters and baserunners out; some of the most common are catching a batted ball
in the air,
tag outs,
force outs, and
strikeouts. After the fielding team has put out three players, that half of the inning is over and the team in the field and the team at bat switch places; there is no upper limit to the number that may bat in rotation before three outs are recorded. Going through the entire order in an inning is referred to as "batting around" and it is indicative of a high-scoring inning. A complete inning consists of each opposing side having a turn (three outs) on offense. The goal of the team at bat is to score more runs than the opposition; a player may do so by batting, then
becoming a baserunner, touching all the bases in order (via one or more plays), and finally touching home plate. A player may also become a baserunner by being inserted as a
pinch-runner. To that end, the goal of each batter is to enable
baserunners to score or to become a baserunner himself. The batter attempts to hit the ball into
fair territory—between the baselines—in such a way that the defending players cannot get them or the baserunners out. In general, the pitcher attempts to prevent this by pitching the ball in such a way that the batter cannot hit it cleanly or, ideally, at all. A baserunner who has successfully touched home plate without being retired (called out) after touching all previous bases scores a
run. In an enclosed field, a
fair ball hit over the fence on the fly is an automatic
home run, which entitles the batter and all runners to touch every base and score. On a field with foul poles, a ball that hits a pole is also a home run. A home run hit with all bases occupied ('
bases loaded') is called a
grand slam.
Fielding team The squad in the field is the defensive team; they attempt to prevent the baserunners from scoring. There are nine defensive positions, but only two have a mandatory location (pitcher and catcher). The locations of the other seven fielders are not specified by the rules, except that at the moment the pitch is delivered, they must be positioned in fair territory and not in the space between the pitcher and the catcher. These fielders often shift their
positioning in response to specific batters or game situations, and they may exchange positions with one another at any time. The nine positions most commonly used (with the number scorekeepers use) are: pitcher (1), catcher (2), first baseman (3), second baseman (4), third baseman (5), shortstop (6), left fielder (7), center fielder (8), and right fielder (9). Note that, in rare cases, teams may use dramatically differing schemes, such as switching an outfielder for an infielder. The numbering convention was established by
Henry Chadwick. The reason the shortstop seems out of order has to do with the way fielders positioned themselves in the early years of the game; the shortstop was positioned in the shallow outfield. Each position is weighted on the
defensive spectrum in terms of difficulty. The most difficult position is the catcher, while the least difficult is first base. Designated hitter, while on the scale, is not part of the defense at all. Pitchers, while part of the active defense, are so specialized in their role that they usually make only routine plays.
The battery The
battery is composed of the
pitcher, who stands on the rubber of the mound, which is also known as the pitching plate, and the
catcher, who squats behind home plate. These are the two fielders who always deal directly with the batter on every pitch, hence the term "battery", coined by
Henry Chadwick and later reinforced by the implied comparison to
artillery fire. The pitcher's main role is to
pitch the ball toward home plate with the goal of getting the batter
out. Pitchers also play defense by fielding batted balls,
covering bases (for a potential
tag out or
force out on an approaching runner), or backing up throws. The catcher's main role is to receive the pitch if the batter does not hit it. Together with the pitcher and coaches, the catcher plots game strategy by suggesting different pitches and by shifting the starting positions of the other fielders. Catchers are also responsible for defense in the area near home plate (such as
dropped third strikes and
wild pitches) or baserunning plays, most commonly when an opposing player attempts to
steal a base. Due to the exceptional difficulty of the position, catchers are universally valued for their defensive prowess as opposed to their ability to hit.
The infielders The four infielders are the
first baseman,
second baseman,
shortstop, and
third baseman. Originally the first, second and third basemen played very near their respective bases, and the shortstop generally played "in" (hence the term), covering the area between second, third, and the pitchers box, or wherever the game situation required. As the game evolved, the fielding positions changed to the now-familiar "umbrella", with the first and third baseman generally positioned a short distance toward second base from their bases, the second baseman to the right side of second base standing further away from the base than any other infielder, and the shortstop playing to the left of second base, as seen from the batter's perspective. The
first baseman's job consists largely of making plays at first base on
ground balls hit to the other
infielders. When an infielder picks up a ball from the ground hit by the
batter, he must throw it to the first baseman who has to catch the ball and maintain contact with the base before the batter gets to it for the batter to be out. The need to do this quickly often requires the first baseman to stretch one of his legs to touch first base while catching the ball simultaneously. The first baseman must be able to catch the ball very well and usually wears a specially designed
mitt. The first baseman fields balls hit near first base. The first baseman also has to receive throws from the pitcher in order to tag runners out who have reached base safely. The position is less physically challenging than the other positions, but there is still a lot of skill involved. Infielders do not always make good throws to first base, so it is the first baseman's job to field any ball thrown toward him cleanly. Older players who can no longer fulfill the demands of their original positions also often become first basemen. The second baseman covers the area to the first-base side of second base and provides backup for the first baseman in
bunt situations. He also is a cut-off for the
outfield. The cut-off provides an intermediary between an outfielder and the infield so that the outfielder does not have to throw the entire distance if they have been forced to field the ball near the outer edge of the outfield. The shortstop fills the critical gap between second and third bases—where right-handed batters generally hit ground balls—and also covers second or third base and the near part of
left field. This player is also a cut-off for the outfield. This position is the most demanding defensively, so a good shortstop doesn't need to necessarily be a skilled batter, though this has changed in modern times. The third baseman's primary requirement is a strong throwing arm, in order to make the long throw across the infield to the first baseman. Quick
reaction time is also important for third basemen, as they tend to see more sharply-hit balls than do the other infielders, thus the nickname for third base as the "hot corner". Also, because there are far more right-handed hitters than lefties, there are more ground balls hit to the left side of the infield due to the natural motion of the batter's swing.
The outfielders The three outfielders,
left fielder,
center fielder, and
right fielder, are so named from the
catcher's perspective looking out onto the field. The
right fielder generally has the strongest arm of all the
outfielders due to the need to make throws on runners attempting to take
third base. The
center fielder has more territory to cover than the corner
outfielders, so this player must be quick and agile with a strong arm to throw balls into the
infield; as with the
shortstop, teams tend to emphasize defense at this position. Also, the
center fielder is considered the
outfield leader, and left- and right-fielders often cede to his direction when fielding
fly balls. Of all outfielders, the
left fielder often has the weakest arm, as they generally do not need to throw the ball as far in order to prevent the advance of any baserunners. The left fielder still requires good fielding and catching skills, and typically receives more balls than the right fielder due to the fact that right-handed hitters, who are much more common, tend to "pull" the ball into left field. Each outfielder runs to "back up" a nearby outfielder who attempts to field a ball hit near both their positions. Outfielders also run to back up infielders on batted balls and thrown balls, including pick-off attempts from the
pitcher or from the
catcher.
Defensive strategy Pitching Effective pitching is critical to a baseball team, as pitching is the key for the defensive team to retire batters and to prevent runners from getting on base. A full game usually involves over one hundred pitches thrown by each team. However, most pitchers begin to tire before they reach this point. In previous eras, pitchers would often throw up to four complete games (all nine innings) in a week. With new advances in medical research and thus a better understanding of how the human body functions and tires out, starting pitchers tend more often to throw fractions of a game (typically six or seven innings, depending on their performance) about every five days (though a few complete games do still occur each year). A single game often requires multiple pitchers, including the
starting pitcher and
relief pitcher(s). Pitchers are substituted for one another like any other player (see above), and the rules do not limit the number of pitchers that can be used in a game; the only limiting factor is the size of the squad, naturally. In general, starting pitchers are not used in relief situations except sometimes during the post-season when every game is vital. If a game runs into many extra innings, a team may well empty its
bullpen. If it then becomes necessary to use a "position player" as a pitcher, major league teams generally have certain players designated as emergency relief pitchers, to avoid the embarrassment of using a less skillful player. In baseball's early years, squads were smaller, and relief pitchers were relatively uncommon, with the starter normally remaining for the entire game unless he was either thoroughly ineffective or became injured. Today, with a much greater emphasis on pitch count, over the course of a single game each team will frequently use from two to five pitchers. In the
2005 ALCS, all four of the
Chicago White Sox victories were complete games by the starters, a highly noteworthy event in the modern game. While delivering the ball, the pitcher has a great arsenal at his disposal in the variation of location, velocity, movement, and arm position (see
types of pitches). Most pitchers attempt to master two or three types of pitches; some pitchers throw up to six types of pitches with varying degrees of control. Common pitches include a
fastball, which is the ball thrown at high speed; a
curveball, which is made to curve by rotation imparted by the pitcher; a
change-up, which seeks to mimic the delivery of a fastball, but arrives at significantly lower velocity; a
splitfinger fastball, which attempts to mimic the delivery of a fastball, but has slight topspin rotation allowing the baseball to sink as it approaches the batter due to the position of the index finger and middle finger being "split" on the baseball; a
slider, which is made to curve laterally by rotation imparted by the pitcher; a
knuckleball, which is held either by the knuckles closest to the nails or by the nails themselves letting the pitcher throw a baseball with little or no spin on the ball allowing the baseball to move in any direction; a
Vulcan changeup, which seeks to mimic the delivery of a fastball, but arrives at a significant lower velocity due to the pitcher holding the baseball with the middle and ring fingers slightly apart; a
circle changeup, which is held in the palm of the hand with the index finger curled around the side of the baseball, allowing the pitcher to mimic the delivery of a fastball, but arrives at a significantly lower velocity. To illustrate pitching strategy, consider the "fastball/change-up" combination: The average major-league pitcher can throw a fastball around , and a few pitchers have even exceeded . The change-up is thrown somewhere between . Since the batter's timing is critical to hitting a pitch, a batter swinging to hit what looks like a fastball, would be terribly fooled (swing and miss, hopefully) when the pitch turns out to be a much slower change-up. Some pitchers choose to throw using the '
submarine style,' a very efficient sidearm or near-underhand motion. Pitchers with a submarine delivery are often very difficult to hit because of the angle and movement of the ball once released.
Walter Johnson, who threw one of the fastest fastballs in the history of the game, threw sidearm (though not submarine) rather than a normal overhand. True underhanded pitching is permitted in Major League Baseball. However, it is difficult to generate enough velocity and movement with the underhand motion. Among modern Major League pitchers,
Chad Bradford had the closest to an underhand delivery, with his knuckles sometimes scraping the ground. However, he is still usually considered a "submarine" pitcher. One example of variation in professional leagues is the use of a
pitch clock, which some leagues use to speed up the game's
pace of play. The rule was first implemented in
college baseball in
2010, and added to certain levels of
Minor League Baseball in 2015. The clock was introduced to Major League Baseball starting in the
2023 Major League Baseball season, establishing a 15 second time limit between pitches with the bases empty, and 20 seconds with at least one baserunner, as well as an automatic ball for violations of the clock. The rule does not exist in other top-level leagues, such as Japan's
Nippon Professional Baseball (NPB), where there exists some resistance to its adoption. South Korea's
KBO League said in 2023 that it would implement a pitch clock "at the earliest possible date."
Fielding strategy , infielders playing "in" for the expected bunt and the possible play at the plate with the
bases loaded Only the pitcher's and catcher's locations are fixed, and then only at the beginning of each pitch. Thus, the players on the field move around as needed to defend against scoring a run. Many variations of this are possible, as location depends upon the situation. Circumstances such as the number of outs, the count (balls and strikes) on the batter, the number and speed of runners, the ability of the fielders, the ability of the pitcher, the type of pitch thrown, the tendencies of the hitter, and the inning cause the fielders to move to more strategic locations on the field. Common defensive strategies include: playing for the bunt, trying to prevent a
stolen base, moving to a shallow position to throw out a runner at home, playing at "
double play depth", and moving fielders to locations where hitters are most likely to hit the ball.
Infield shifts were restricted by the OBR starting in 2023, which mandated that two infielders must be positioned on either side of second base before each pitch is thrown. Note that this did not violate baseball's permanent substitution rule in any way, as at no time did either player leave the game. This "permanent substitution" rule is in contrast to some other sports, such as basketball, hockey and American football, that practice "free substitution". In some cases, if the defensive manager responds to the entrance of a pinch-hitter by bringing in a new pitcher, the pinch-hitter may be replaced by another pinch-hitter without having come to the plate, in which case the first pinch-hitter is considered to have entered the game and is ineligible to do so later. However, the defensive manager may not replace a pitcher who has not pitched to at least one batter (three batters in MLB as of 2020), except in case of injury. The reentry of a replaced player into the game is a violation of the permanent substitution rule; if the defense has more than nine players on the field at any time, the umpire must determine who is the tenth player, and that player is ejected from the game. Many
amateur leagues allow a starting player who was removed to return to the game in the same position in the batting order under a re-entry rule. Youth leagues often allow free and open substitution to encourage player participation.
Pitchers as batters, and the designated hitter Pitching is a specialized skill, particularly in the collegiate and professional ranks; so most pitchers are relatively poor hitters, or, those who were skilled batsmen are simply unable to adequately hone their hitting skills to be comparable to regular position players. As a result, unless keeping a given pitcher in the game is a higher priority than the prospect of immediate offense, it is common to substitute for a pitcher when he is due to bat. This pinch hitter is often then replaced by a relief pitcher when the team returns to the field on defense. A more complicated tactic is the
double switch, in which a pitching change is accompanied by the simultaneous replacement of another fielder. If the pitcher is due to bat soon, and the outgoing fielder batted recently, the new pitcher will take the outgoing fielder's place in the batting order, thus delaying his next time at bat. A common variation on this involves the introduction of a player who has just pinch hit (or pinch run for the pinch hitter) into the defensive alignment; unless this player becomes his team's next pitcher, another field player departs the game, and the new pitcher then assumes that player's place in the batting order. Many leagues allow
designated hitters, notably
Major League Baseball's
American League (which instituted the Designated Hitter in 1973 to boost offensive output). A designated hitter (or DH) is a player whose sole purpose is to hit when it would normally be the pitcher's turn (or, in some leagues, if the pitcher is a good batter, another weaker batter). This is not considered a substitution, but rather a position, albeit a purely offensive one. A designated hitter does not play in the field on defense and may remain in the game regardless of changes in pitchers. If the designated hitter is moved to a fielding position, the team loses the DH, and the fielder whose position was taken by the former DH is replaced by the pitcher, who assumes that player's position in the hitting lineup. The use of the designated hitter, which reduces the need for complicated strategy like the double-switch, is opposed by many baseball traditionalists. Nevertheless, it is used today at most levels of baseball in the United States and abroad.
Major League Baseball's
National League was the most prominent league that required pitchers to bat, until allowing the designated hitter beginning with the 2022 season.
Rosters The number of players on a major league roster is dictated by the labor agreements worked out between players and management. According to prior rules, a team may have a maximum of 25 men on a roster from Opening Day until August 31. Beginning in the 2012 season, a major league team was allowed to carry a 26th man on its roster when playing the second game of a double-header that was scheduled at least 48 hours in advance. As of 2020, the number has been increased to 26, of whom no more than 14 may be pitchers, with 27 for a doubleheader. After August 31, during the regular season teams may call up additional personnel to the active roster, up to a maximum of 40 players. This number is rarely actually approached, however, with most teams' September rosters peaking at around 30 players. In 2020, the number was limited to 28. In the postseason, rosters are fixed at 25 men. Until 2007, teams could not replace players on their playoff rosters in the event of an injury and had to play out the series shorthanded. Starting in 2007, an injured player could be placed on the disabled list and replaced by another player who was not included on the initial 25-man roster, but the injured player becomes available for the next round of the playoffs should his team advance. This rule applies in most circumstances. ==See also==