The batting order or batting lineup is the sequence in which the nine members of the offense take their turns in batting against the pitcher. The batting order is the main component of a team's offensive strategy.
In modern American baseball, some batting positions have nicknames: leadoff for first, cleanup for fourth, and last for ninth. Others are known by the ordinal numbers or the term #-hole (3rd place hitter would be 3-hole). In similar fashion, the third, fourth, and fifth batters are often collectively referred to as the heart or meat of the batting order, while the seventh, eighth, and ninth batters are called the bottom of the lineup, a designation generally referring both to their hitting position and to their typical lack of offensive prowess.
At the start of each inning, the batting order resumes where it left off in the previous inning, rather than resetting to start with the #1 hitter again. While this ensures that the players all bat roughly the same number of times, the game will almost always end before the last cycle is complete, so that the #1 hitter (for example) almost always has one plate appearance more than the #9 hitter, which is a significant enough difference to affect tactical decisions. 
Positions in the lineup
The first player in the batting order is known as the leadoff hitter. The leadoff batter is traditionally an individual with a high on-base percentage, plate discipline, bat control, good speed, and the ability to steal bases. His goal is to ensure the team has baserunners when the later, more powerful hitters come to bat. Once on base, his main goal is to get into scoring position (that is, 2nd or 3rd base) as quickly as possible, either through steals, hit and run plays or intelligent baserunning decisions, and then on to score.
The second batter is usually a contact hitter with the ability to bunt or sacrifice a baserunner over or get a hit. His main goal is to move the leadoff man into scoring position and to avoid grounding into double plays. Managers often like to have a left-handed hitter bat second because of the potential gap in the infield defense caused by the first baseman holding the leadoff batter.
The third batter, in the three-hole, is generally the best all-around hitter on the team, often hitting for a high batting average but not necessarily very fast. Part of his job is to reach base for the cleanup hitter, and part of it is to help drive in baserunners himself. Third-place hitters are best known for "keeping the inning alive".
The fourth player in the batting order is known as the cleanup hitter, and in modern baseball is almost always one of the best hitters on the team, often the one with the most power and ability to drive in runs with extra-base hits (double, triple, or home run). His main goal is to drive in runs, although he is expected to score runs as well. Hitting cleanup requires an exceptional level of talent, and the ability to deliver big hits in important situations (such as the bases loaded with two out).
The theory behind the cleanup hitter is that, at the beginning of the game, if at least one of the first three batters reaches base with a single-base hit or walk, a home run will result in two or more runs rather than just one (a "solo" home run). If all three players reach base, thereby loading the bases, the cleanup hitter has the chance to hit a grand slam, scoring four runs. But even without the grand slam, this batter can extend an inning with a high batting average and frequent walks.
The fifth and sixth (and sometimes seventh) batters have traditionally been RBI men, with the main goal of driving runners home, especially with sacrifice flies. The 3rd, 4th and 5th hitters in the lineup are called the "heart of the order", signifying their collective ability to get on base, hit for power and drive in runs. The fifth batter is usually a team's second-best power hitter, and his purpose is often to "protect" the clean-up hitter in the batting order. He is expected to pose enough of a threat that the opposing team refrains from intentionally walking the clean-up hitter in potential scoring situations. The sixth hitter serves as a backup to the fifth hitter in case he fails to score runs or to drive more in himself if another scoring opportunity presents itself.
The seventh and eighth batters are often not as powerful as the earlier batters, and do not have as high a batting average. They are often players who are in the lineup more because of their defensive ability (typically catcher, second baseman or shortstop) than their ability as hitters. They are still expected to produce (as is the case for any regular starter), but they have less pressure in those spots.
In the presence of the designated hitter, the ninth batter is often like the second leadoff. Nine-hitters tend to be fast, and have a decent on-base percentage like the leadoff hitter.
- In Japan, the cleanup hitters include batters 3, 4, and 5.
- As early as 1892, it was recognized that a left-handed hitter in the second spot would make it easier for a man on base to steal second.