Tagging and Forcing
When a batter hits a ball in fair territory he can get out in three ways. First, if a fielder catches the ball in the air. Second, if he is forced at first base - when a ball hit on the ground is relayed to first base before he gets there (the fielder has to touch the base with any part of his body while holding the ball). Or third, if he is tagged. Other runners can also be judged out for the same reasons. But, they can also be forced out. For example, a runner at first base has to run to second base if a better hits a ball along the ground and starts running to first base himself (and if second base is loaded with a runner, that runner will have to run too). If the ball gets to second base before he does, or if he's tagged, he's out.

If a runner is not forced to run - for example, he's on second base with no runner behind him on first base - and he chooses to advance he can only be put out by being tagged.

The Run of the Game
The game is played in nine innings, with each team batting once in each inning. By tradition born out of courtesy, the visiting team always bats first in the top half of the inning. This is because the visiting team is listed on the top half of the scoreboard - and the home team bats last, which gives the home players a chance to rescue the game if necessary so that they can send their fans home happy.

Each inning lasts until each side has registered three outs. The players from each team bat in an order that is decided before the start of the game and can't be changed - other than in certain circumstances. However, in many league, the pitcher can be replaced in the batting order by a designated hitter, who takes the place of the pitcher whenever his turn comes to bat. The batting order is carried over from innign to inning - so if batter number three makes the last out of the first inning, batter number four will lead off the second inning.

Pinch Hitters and Relievers
Players and be substituted at any time, but once taken out of the game, a player cannot return. Pinch hitters and pinch runners are often used, as are defensive replacements by the team with the lead in the later innings. Pitchers rare;y pitch the entire game, so the starting pitcher will be replaced when he tires or begins to throw ineffectively - or even taken off to spare his arm for his next game (it normally takes a pitcher's arm several days to recover). Relief pitchers are also used to get 'platoon advantage': it's harder for a left-handed better to hit a left-handed pitch, because he has less time to see the ball coming across the pitcher's body; and the same thing is true of right handed batters and right-handed pitchers. It's no good putting a left-handed pitcher against a switch hitter - one of these can bat either right or left-handed.

Most teams also have a 'closer': a relief pitcher who only plays in the last inning or two of the game when his team has a close lead to preserve. A starting pitcher who works the full nine innings is said to have pitched a 'complete game'; and if the other team fails to score, he's pitched a 'shutout'.

The Teams
Major League teams have rosters of 25 men, with 10 or 11 pitchers and 14 to 15 field players. Most teams will use a 'rotation' of five starting pitchers, so a starter need only pitch once every five days.

Each team has a manager and four or five coaches: one looks after the pitchers; another organises the 'bull pen', where relief pitchers wait to be called on and warm-up. When the team is batting, two coaches are stationed along the baselines - one near first and one near third - to relay signs to the hitter and runners and tell them whether they can continue running, without the player losing time during his run by having to look up at the fielded ball.

The Umpires
There are four umpires on the field, the key one being the home-plate umpire, who calls balls and strikes. The other umpires are stationed around the three other bases, to call the plays at each base, to determind fair and foul balls down the baselines, and to watch the pitcher and batter form the front - the home-plate umpire, crouched behind the catcher can't do this. In post-season play, two additional umpires watch the foul lines in the left and right field.