Baseball rules and personnel
More baseball rules
Each team is allowed to substitute for any player at any time, but no player, once removed from the game, can return. It is very common for a pitcher to pitch for several innings and then be removed in favor of a relief pitcher. Also, because pitching is a specialized skill, many pitchers are not good hitters, so it is common to substitute for a pitcher when his team is at bat. This can be done by inserting a pinch hitter who replaces the pitcher for his time at bat, and who is in turn replaced by a relief pitcher when the team returns to the field on defense. Most leagues (notably Major League Baseball's American League) also allow a designated hitter, a player whose sole purpose is to hit when it would normally be the pitcher's turn. A designated hitter does not play in the field on defense, and may remain in the game regardless of changes in pitchers.
Many amateur leagues will allow a starting player who was removed to return to the game in the same position in the batting order under the re-entry rule. In nearly all adult leagues, substitutes cannot return once removed. Youth leagues often allow free and open substitution to encourage player participation.
Pinch Hitter also refers generally to any substitute batter who has not previously appeared on the field. Similarly, a pinch runner may be used to substitute for any baserunner.
Running the bases
A runner who is entitled to occupy a base and has not been displaced may not be tagged out with the ball. Runners may attempt to advance from base to base on any fair ball that touches the ground. 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 occupy (tag up) after the ball is caught. Once they do this, they may attempt to advance at their own risk.
Baserunners may attempt to advance while the pitcher is throwing a pitch. The catcher (or pitcher, in lieu of delivering the pitch) often tries to prevent this by throwing the ball to one of the infielders in order to tag the runner. This pick-off attempt is usually unsuccessful in tagging out the runner but is effective in keeping the runner closer to the base. If the runner is tagged out while diving back to the base, it is called a pick-off. If the runner attempts to advance to the next base but is tagged out before reaching it safely, he is caught-stealing. A successful attempt by the runner is called a stolen base. If a pitch gets away from the catcher, runners may also try to advance. This may be a wild pitch, if the pitcher is held responsible for the ball getting away, or a passed ball if the catcher is deemed to be at fault.
The standard dimensions of a baseball field, with 90 feet between bases, generate many close baserunning plays. On one hand, an infielder who cleanly fields a ball hit on the ground, then throws it quickly and accurately, will usually get the ball to a base before the runner reaches it. However, any hesitation or mistake on the part of the fielder may allow the runner to reach the base safely.
Other Baseball personnel
Each team is run by a manager, whose primary responsibility during the game is to assign players to fielding positions, determine the lineup, and decide how to substitute players. Managers are also assisted by coaches in helping players to develop their skills.
Any baseball game involves one or more umpires, who make rulings on the outcome of each play. At a minimum, one umpire will stand behind the catcher, to have a good view of the strike zone, and call each pitch a ball or a strike. Additional umpires may be stationed near the bases, thus making it easier to see plays in the field.
Another figure in baseball worth noting is the official scorer. The results of baseball games are summarized in tables called box scores. The scorer is responsible for a number of judgments that go into the boxscore. For example, if a batted ball is misplayed by a fielder, the scorer may choose to charge the fielder with an error instead of crediting the batter with a hit. Within certain guidelines, the scorer also determines which pitchers are credited with winning and losing the game, and whether a relief pitcher will be awarded a save.