Baseball is a sport played between two teams of nine players each. The offensive action is hitting a pitched ball with a bat and then running the bases. The winner is the team scoring the most runs.

Teams of nine active players and a varying number of reserves hit a small leather ball with a wooden bat, in an attempt to advance around the bases, and ultimately score runs. Pitchers deliver the ball to batters from a set distance, while fielders attempt to throw the ball towards a base before a runner arrives.

Score more runs than the opposing team before the end of the 9th inning.

The field of play can have varying dimensions, with the exception of the distance between the bases (90 feet) and the distance between the pitchers mound and home plate (60 feet 6 inches). Teams alternate between hitting and fielding for nine innings, with players hitting in a constant order. Players can be substituted during the game, but cannot return. Teams must bat and play the field during each inning. Once three outs have been recorded, the teams switch sides. If a game is tied at the end of nine innings, teams play extra innings until the tie is broken.

Though the earliest documented play of baseball-like games go back to the mid-18th century, baseball as it is known today wasn't played until a century later. Around that time, pro and semi-pro leagues formed in the United States, culminating with the formation of the National League, the first Major League. By the beginning of the 20th century, the American League was created, rules were formalized and the World Series to determine a baseball champion was established. Throughout the 20th century baseball spread to become popular in western Europe, the Caribbean, central and South America, east Asia and Australia.

Ball
Bases
Bat
Glove

Injuries are most likely to occur to pitchers, specifically, to their throwing arms, as throwing a baseball puts great strain on a pitcher's shoulder and elbow.

Training depends greatly on a player's position. Pitchers require strong legs and throwing arms, and train to developed endurance in both. Offensive players rely on a developed upper body in order to generate power while hitting, while primarily defensive players train for speed and agility for fielding.

Base - one of four stations that must be reached in order to score a run

Fair - within the field of play

Foul - outside the field of play

Hit - a ball hit such that the batter can advance safely to a base
without aid

Home Plate - flat, five-sided, rubber base in which must be touched in order to score

Out - having had one's turn ended by the team on the field

Run - a point scored by touching home plate after touching all other bases

http://en.wikipedia.org/wiki/Baseball