Let's follow one pitch. The pitcher throws the ball and the batter tries to hit it with the bat. The pitching rubber is 60 feet, 6 inches from home plate. The pitcher throws, the batter swings, and the play begins.

Not every pitch is a good one to swing at. The strike zone is the area over home plate between the middle of the batter's body and the kneecaps. The umpires enforce the rules. They decide if a pitch is a strike or a ball. They also decide if a runner is safe or out.

Balls and strikes add up. A ball is a pitch outside the strike zone that the batter does not swing at. A batter who gets four balls walks to first base. Three strikes make a strikeout. A foul ball counts as a strike, unless the batter already has two strikes.

When the batter does hit the ball, it is a hit. The four kinds of hits are singles, doubles, triples and home runs. Hitters keep a number called batting average. It is a batter's hits divided by his times at bat. A designated hitter, or DH, bats in place of the pitcher.

On a home run, the batter goes around all the bases and scores. So does every runner already on base. The bases are 90 feet (27 meters) apart. A runner can also move on his own. A stolen base happens when a runner moves up to the next base, not because of a hit.

The defense gets outs too. A batter is out if the ball is caught. He is also out if the ball is thrown to first base before he gets there. A double play is a play in which two runners or batters are put out. Three outs end a team's turn at bat.

A game is divided into nine innings. In each inning, each team bats once: one team in the top half and the other in the bottom half. If the game is tied after nine innings, extra innings are played until one team is ahead.

Words to know

• pitcher: throws the ball
• umpires: game judges
• strikeout: three strikes
• innings: parts of play
• average: hits divided