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.
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 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." 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 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 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." 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.