The ultimate goal of the team at bat is to score runs. To accomplish this feat, the team at bat successively (in a predetermined order called a lineup or batting order) sends its nine players to the batter’s box (adjacent to home plate) where they become batters. (Each team sets its batting lineup at the beginning of the game. Changes to the lineup 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 or an “at-bat.” Batters advance to the bases in a variety of ways: hits, walks, hit-by-pitch, and a few others. 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 or not the ball is hit over the fence. 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 fielder to catch it on its descent. A line drive is like a fly ball, but the ball is hit with such force that its trajectory seems level to the ground. A batted ball which is not hit into the air, and which touches the ground within the infield before it can be caught, is called a ground ball. When a ball is hit outside the foul line, it is a foul ball, requiring the batter and all runners to return to their respective bases.
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.
When a runner reaches home plate, he scores a run and is no longer a base runner. He must leave the playing area until his spot in the order comes up again. A runner may only circle the bases once per plate appearance and thus can score no more than a single run.