A full baseball team consists of 10 players: nine batters plus a pitcher, who does not bat. When a team is not up to bat, eight of the batters join the pitcher in the field to play defense. The ninth batter, known as the designated hitter (DH), remains in his team’s dugout on defense. At the 2020 Olympics, teams are allowed 14 alternates, to be split between batters and pitchers. 

A baseball game is contested over nine untimed innings. Each inning is divided into two half-innings, known as the “top half” and the “bottom half”. During the top half of an inning, the home team pitches and plays defense while the away team bats offensively. During the bottom half, the reverse takes place. A half-inning lasts as long as it takes for the batting team to make three outs. If a game is tied after nine innings, extra innings are played until one team ends an inning with the lead. 

The object of baseball is to score more runs than the opposing team in nine innings. A run is scored when a player from the batting team manages to safely round all four bases, touching home plate. The simplest (and most dramatic) way for a player to score a run is to hit a pitch over the outfield fence for a “home run”, allowing that player round the bases unchallenged. Though while simple, home runs are infrequent. Most runs are scored when multiple batters from one team string together hits or walks in close succession, before making three outs, allowing base runners to advance around the bases and touch home plate safely. 

When an offensive player comes to bat, one of two things can happen: he can make an out or he can get on base. The most common way to get on base is to hit a pitch so that it lands safely in the field of play, and so that the batter can run 90 feet to first base, before the ball is fielded and thrown to the first baseman. This is known as getting a “hit”. A batter can also be awarded first base automatically if he is hit by a pitch, or if the pitcher throws four balls outside the strike zone during the plate appearance (known as a “walk”). Most elite batters reach base 35-45% of the time. 

The most common outcome of a plate appearance is that the hitter makes an out. If the batter hits a ball that is caught on the fly by a member of the fielding team, or if a ground ball is fielded and thrown to the first baseman before the batter can run to the base, or if the batter is tagged out at any point while in between bases, he is out. Alternatively, if the batter sees three strikes during the plate appearance before putting the ball in play or taking a walk, he has struck out. 

The pitcher is the most important defender on the field, and has the most to do with the outcome of a ballgame. The pitcher pitches the ball toward the batter in hopes of forcing the batter into making an out. The pitcher aims for the strike zone, an imaginary vertical, two-dimensional rectangle spanning the width of home plate and the height of the area between the batter’s knees and his center-chest. A “strike” occurs when the batter swings at a pitch, regardless of its location, and misses, or if the batter does not swing at a pitch that crosses the strike zone. Three strikes, you’re out. 

If the pitcher misses the strike zone with a pitch, and the batter does not swing, it is a “ball”. Four balls in one plate appearance triggers a walk. 

The pitcher’s ultimate goal, with the help of his fielders, is to allow as few runs as possible over nine innings. Most games, the pitcher who starts the game for his team is replaced by a relief pitcher midway through. However, on rare occasions one pitcher will pitch the entire game for his team, allowing no hits, in what is called a “no-hitter”. On the rarest – and most celebrated – of occasions, a pitcher will allow no baserunners at all, known as a “perfect game.”