Understanding Baseball

General Structure
Innings and Scoring
The Catcher
Fielding Team
Defensive Strategy
Batting Team
Batting and Base Running Strategy
Substitutions

General Structure
Baseball is played between two teams of nine players each, under the authority of one or more umpires. There are usually four umpires in major league games; up to six (and as few as one).

There are four bases, numbered counter-clockwise, the first, second and third bases are cushions shaped as 38cm squares which are raised a short distance above the ground; together with home plate, the fourth base, they form a square with sides 27.4m called the diamond. The home plate is a pentagonal rubber slab known as simply home.

The playing field is divided into three main sections:
- Infield: containing the four bases, is for general defensive purposes bounded by the foul lines and within the grass line.
- Outfield: the grassed area beyond the infield grass line between the foul lines, and bounded by a wall or fence.
- Foul territory: the entire area outside the foul lines.

The pitcher's mound is located in the centre of the infield. It is 5.5m diameter mound of dirt no higher than 25.4cm. Near the centre of the mound is the pitching rubber, a rubber slab positioned 18.4m 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.
Innings and Scoring
An inning is broken up into two halves in which the away team bats in the first (top) half, and the home team bats in the second (bottom) half.

In baseball, the defence always has the ball — a fact that differentiates it from most other team sports.

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 from the opposing team, 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". It is indicative of a high scoring inning. A complete inning consists of each opposing side having a turn (three outs) on offense.

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. 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 during the entire pitch, so he can only take one step backward and one forward in delivering the ball.

The goal of the team at bat is to score more runs than the opposition; a player may do so only by batting, then becoming a baserunner, touching all the bases in order (via one or more plays), and finally touching home plate. To that end, the goal of each batter is to enable baserunners to score or to become a baserunner themself. The batter attempts to hit the ball 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 successfully touches home plate without being tagged out after touching all previous bases in order scores a run. In an enclosed field, a fair ball hit over the fence on the fly is normally an automatic home run, which entitles the batter and all runners to touch all the bases and score. A home run

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. 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 thereafter, play stops and the home team is declared the winner.
The Catcher
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 that signal to the pitcher what pitch to throw and where. If the pitcher disagrees with the call, he will "shake off" the catcher by shaking his head; he accepts the sign by nodding. Each team has a different set of signals, though the number 1 is almost universal as a fast ball. 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.

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. 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 during the entire pitch, so he can only take one step backward and one forward in delivering the ball.
Fielding Team
The team 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 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 are: pitcher, catcher, first baseman, second baseman, third baseman, shortstop, left fielder, centre fielder and right fielder.

- The Battery: is composed of the pitcher and the catcher. These are the two fielders who always deal directly with the batter on every pitch, hence the term "battery". The pitcher's main role is to pitch the ball toward home plate with the goal of getting the batter out. Pitchers also play defence by fielding batted balls, covering bases, 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 defence in the area near home plate

- The Infielders: the four infielders are the first baseman, second baseman, shortstop and third baseman. The first and third baseman are generally positioned a short distance toward second base from their bases, the second baseman to the right side of second base standing farther 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, filling in the gaps.
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 must 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 second baseman covers the area to the first-base side of second base and provides backup for the first baseman.
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 position is the most demanding defensively.
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 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 are: left fielder, centre fielder and right fielder. 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 centre 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 in to the infield; as with the shortstop, teams tend to emphasize defence at this position. Also, the centre fielder is considered the outfield leader.
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 tends to receive 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:
Pitching is the key for the defensive team to retire batters and to preventing 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, starting pitchers tend more often to throw fractions of a game (typically six or seven innings, depending on their performance) about every five days.
Multiple pitchers are often needed in a single game, including the starting pitcher and relief pitcher(s). Pitchers are substituted for one another like any other player, and the rules do not limit the number of pitchers that can be used in a game.
If a game runs into many extra innings, it may becomes necessary to use a "position player" as a pitcher, major league teams generally have certain players pre-designated as emergency relief pitchers, to avoid the embarrassment of using a less skilful player.
While delivering the ball, the pitcher has a great arsenal at his disposal in the variation of location, velocity, movement, and arm location. Most pitchers attempt to master two or three types of pitches. 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; and a change-up, which seeks to mimic the delivery of a fastball but arrives at significantly lower velocity.
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. True underhanded pitching is permitted in Major League Baseball. However, it is difficult to generate enough velocity and movement with the underhand motion.

Fielding Strategy
Only the pitcher's and catcher's locations are fixed, and then only at the beginning of each pitch. 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.
Batting Team
Batters and Runners
The ultimate goal of the team at bat is to score runs. To accomplish this task, the team at bat successively (batting order) sends its nine players to the batter's box. Each team sets its batting order at the beginning of the game. Changes to the order are tightly limited by the rules of baseball and must be communicated to the umpires, who have the substitutions announced for the opposing team and fans.
A batter's turn at the plate is called a plate appearance. Batters can advance to first base safely in one of seven methods: a base-hit or walk are by far the most common; being hit-by-the-pitch, reaching by error or fielder's choice are less common; and somewhat rarely a player may reach base by virtue of interference or a passed ball on a strike-out, where the player is allowed to run and reach base safely if he can.
When the batter hits a fair ball, he must run to first base, and may continue or stop at any base unless he is put out. A successful hit occurs when the batter reaches a base: reaching only first base is a single; reaching second base, a double; third base, a triple; and a hit that allows the batter to touch all bases in order on the same play is a home run - whether the ball is hit over the fence does not matter (if the ball is not hit over the fence and the batter touches all bases, it is usually referred to as an "inside-the-park home run").
Once a runner is held to a base, he may attempt to advance at any time, but is not required to do so unless the batter or another runner displaces him (called a force play). A batter always drops his bat when running the bases; otherwise, the bat would slow him down and could give rise to a call of interference if it were to contact the ball or a fielder.
Depending on the way the ball comes off the bat, the play has different names. A batted ball is called a fly ball if it is hit in the air in an upward arc, such that a fielder might be able to catch it before it hits the ground. A batted ball is called a ground ball if it hits the ground within the infield before it can be caught, often due to being hit in a downward trajectory. Several different names are used to describe fly balls, depending on their trajectory. A ball hit high in the air and seemingly almost straight up is called a "pop-up". A ball hit forcefully in a fast-moving and seemingly almost straight-line trajectory is called a line drive. A "shallow" fly ball, hit with just enough force to possibly land between the infielders and the outfielders, is often call a "blooper". A "deep" fly ball is hit with enough force to approach and possibly clear the outfield fence.
When a ball is hit outside the foul lines, it is a foul ball, requiring the batter and all runners to return to their respective bases, whether it is caught or not.
Once the batter and any existing runners have all stopped at a base or been put out, the ball is returned to the pitcher, and the next batter comes to the plate. After the opposing team bats in its own order and three more outs are recorded, the first team's batting order will continue again from where it left off.
Batting
Each plate appearance consists of a series of pitches, in which the pitcher throws the ball towards home plate while a batter is standing in the batter's box.
With each pitch, the batter must decide whether to swing the bat at the ball in an attempt to hit it. The pitches arrive quickly, so the decision to swing must be made in less than a tenth of a second, based on whether the ball is hittable and in the strike zone, a region defined by the area directly above home plate and between the hollow beneath the batter's knee and the midpoint between the top of the shoulders and the top of the uniform pants. In addition to swinging at the ball, a batter who wishes to put the ball in play may hold his bat over home plate and attempt to tap a pitch lightly; this is called a bunt. Good bunting technique has been described as "catching the ball with the bat."
On any pitch, if the batter swings at the ball and misses, he is charged with a strike. If the batter does not swing, the home plate umpire judges whether the ball passed through the strike zone. If the ball, or any part of it, passed through the zone, it is ruled a strike; otherwise, it is called a ball. The number of balls and strikes thrown to the current batter is known as the count; the count is always given balls first, and then strikes.
If the batter swings and makes contact with the ball, but does not put it in play in fair territory (foul ball) he is charged with an additional strike, except when there are already two strikes. A foul ball with two strikes leaves the count unchanged.
If a pitch is batted foul or fair and a member of the defensive team is able to catch it, before the ball strikes the ground, the batter is declared out. In the event that a bat contacts the ball, but the ball continues sharply and directly to the catcher's mitt and is caught by the catcher, it is a foul tip, which is same as an ordinary strike.
When three strikes occur on a batter, it is a strikeout and the batter is automatically out unless the pitch is not caught by the catcher or if the pitch bounces before it is caught. It is then ruled an uncaught third strike, a violation of the third strike rule. If the catcher drops the third strike the batter is permitted to attempt to advance to first base. In this case, the batter is not out (although the pitcher is awarded a strikeout). The catcher can try to get the batter out by tagging him with the ball or throwing the ball to first base to put him out.
On the fourth ball, it is called a walk, and the batter becomes a runner, and is entitled to advance to first base without risk of being put out, called a base on balls or a walk. If a pitch touches the batter (or the batter's clothes), the umpire declares a hit by pitch and the batter is awarded first base, unless the umpire determines that the ball was in the strike zone when it hit the batter, or that the batter did not attempt to avoid being hit. In practice, neither exception is ever called unless the batter obviously tries to get hit by the pitch. In addition, if the batter swings at a pitch that hits him, it counts as a strike. If the catcher's mitt, catcher's mask, or any part of the catcher comes in contact with the batter and/or the batter's bat as the batter is attempting to hit a pitch, the batter is awarded first base, ruled "catcher's interference".

Baserunning
Once a batter becomes a runner and reaches first base safely, he is said to be "on" that base until he attempts to advance to the next base, until he is put out, or until the half-inning ends. When comparing two or more runners on the basepaths, the runner farther along is called a lead runner or a preceding runner; the other runner is called a trailing runner or a following runner. Runners on second or third base are considered to be in scoring position since ordinary hits, even singles, will often allow them to score.
A runner legally touching a base is "safe"—he may not be put out. Runners may attempt to advance from base to base at any time (except when the ball is dead), but must attempt to advance when forced--when all previous bases are occupied and the batter becomes a runner. When a ball is hit in the air, a fly ball, and caught by the defending team, runners must return and touch the base they occupied at the time of the pitch (tagging up) after the ball is first touched by a fielder. Once they do this, they may attempt to advance at their own risk.
Only one runner may occupy a base at a time; if two runners are touching a base at once, the trailing runner is in jeopardy and will be out if tagged, unless he was forced--in which case the lead runner is out when tagged for failing to reach his force base. Either such occurrence is very rare.
After a play, at most three runners may be on the basepaths, one on each base--first, second, and third. When three runners are on base, this is called bases loaded.
Baserunners may attempt to advance, or steal a base, while the pitcher is throwing a pitch. The pitcher, in lieu of delivering the pitch, may try to prevent this by throwing the ball to one of the infielders in order to tag the runner; if successful, it is called a pick-off.
If the runner attempts to steal the next base but is tagged out before reaching it safely, he is caught stealing. An illegal attempt by the pitcher to deceive a runner, among other pitching violations, is called a balk, allowing the runners to advance one base without risk of being put out.
Another fundamental tenet of the rules of baseball is that a runner originally ruled out can subsequently be ruled safe, but once a runner is ruled safe he cannot be called out on the same play, unless the baserunner overruns their base.
Batting and Base Running Strategy
The goal of each batter is to become a base runner himself or to help move other base runners along.
Batters attempt to "read" pitchers through pre-game preparation by studying the tendencies of pitchers and by talking to other batters that previously faced the pitcher. While batting, batters attempt to "read" pitches by looking for clues that the pitcher or catcher reveal. These clues include movements of the pitcher's arms, shoulders, body, etc, or the positioning of the catcher's feet and glove. Batters can attempt to "read" the spin of a ball early in the pitch to anticipate its trajectory.
In general, base running is a tactical part of the game requiring good judgment by runners to assess the risk in attempting to advance. During tag plays, a good slide can affect the outcome of the play. Managers will sometimes simultaneously send a runner and require the batter to swing in an attempt to advance runners. On a hit-and-run play the batter will often try to hit to the opposite field. Hitting to the opposite field will likely find an opening in the infield vacated by the fielder covering second base. This is because coverage of second base against a steal is best achieved by whichever fielder is closer to second base, the shortstop or the second baseman; and such positioning is aimed at defending against the natural tendency of the hitter.
During the course of play many offensive and defensive players run close to each other, and during tag plays, the defensive player must touch the offensive player. Although baseball is considered a non-contact sport, a runner may be allowed to make potentially dangerous contact with a fielder as part of an attempt to reach base, unless that fielder is fielding a batted ball.
A good slide is often more advantageous than such contact, and "malicious" contact by runners is typically prohibited as offensive interference. The most common occurrence of contact of this nature is at home plate between the runner and the catcher, as the catcher is well padded and locked into position that completely blocks home plate from the runner, and the runner will often try to knock the ball out of the catcher's hand by running him over. Since the catcher is seen (symbolically and literally) as the last line of defence, it seems natural that the more physical play happens here.
Substitutions
Each team is allowed to substitute for any player at any time the ball is dead. A batter who replaces another batter is referred to as a pinch hitter; similarly, a pinch runner may be used as a replacement for a baserunner. Any player who replaces another player between innings is known as a "defensive replacement". Any replacement is a permanent substitution; the replaced player may not return to the game.

It is common for a pitcher to pitch for several innings and then be removed in favour of a relief pitcher. Because pitching is a specialized skill, most pitchers are relatively poor hitters; it is common to substitute for a pitcher when he is due to bat. This pinch hitter is typically then replaced by a relief pitcher when the team returns to the field on defence, but more complicated substitutions are possible, most notably the double switch.

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.

The designated hitter is a player whose sole purpose is to hit when it would normally be the pitcher's turn. 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 defence 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 order.
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