The squad in the field is the defensive team; they attempt to prevent the baserunners from scoring. There are nine defensive positions, however, only two of the positions have a mandatory location (pitcher and catcher), the locations of the other seven fielders is 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, center fielder, and right fielder. Note that, in rare cases, teams may use dramatically differing schemes, such as switching an outfielder for an infielder. Scorekeepers label each position with a number starting with the pitcher (1), catcher (2), first baseman (3), second baseman (4), third baseman (5), shortstop (6), left fielder (7), center fielder (8), right fielder (9). This 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 battery is composed of the pitcher, who stands on the rubber of the mound, 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.
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 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 force 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 while maintaining contact with the base before the batter gets to the base for the batter to be out. The first baseman must be able to catch the ball very well and usually wears a specially designed mitt. The first baseman also 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 don’t 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. This is when the outfielder doesn’t have to throw the full distance from him/her to the base, but just to the cut-off. 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 good batter. 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.”
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 in to 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 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. The left fielder also backs up third base on pick-off attempts from the catcher.
Effective pitching is vitally important to a baseball team, as 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. 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 6 or 7 innings depending on their performance) about every five days (though a few complete games do still occur each year).
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 (see below), 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 pre-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 (100 being the “magic number” in general), 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.
Although a pitcher can only take one step backward and one forward 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; some pitchers throw up to 6 types of pitches with varying degrees of control. Common pitches include a fastball, which is the ball thrown at just under maximum velocity; 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.
To illustrate pitching strategy, consider the “fastball/change-up” combination: The average major-league pitcher can throw a fastball around 90 miles per hour (145 km/h), and a few pitchers have even exceeded 100 miles per hour (161 km/h). The change-up is thrown somewhere between 75 to 85 miles per hour (121 to 137 km/h). 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 fast balls in the history of the game, threw sidearm (though not submarine) rather than a normal overhand. True underhanded pitching is not illegal in Major League Baseball. However, it is difficult to generate enough velocity and movement with the underhand motion.
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, and the inning cause the fielders 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.