The squad in the field is the defensive team. They attempt to prevent the baserunners from scoring. There are nine defensive positions, but only two have a mandatory location (pitcher and catcher). The locations of the other seven fielders is not specified by the rules, except that at the moment the pitch is delivered they must be positioned in fair territory and not in the space between the pitcher and the catcher. These fielders often shift their positioning in response to specific batters or game situations, and they may exchange positions with one another at any time.
→ Main article: Positions
The nine positions most commonly used are: Pitcher (1), Catcher (2), First Baseman (3), Second Baseman (4), Third Baseman (5), Shortstop (6), Left Fielder (7), Center Fielder (8), and Right Fielder (9).
→ Main article: Pitches
In baseball, a pitch is the act of throwing a baseball toward home plate to start a play. The biomechanics of pitching have been studied extensively. The phases of throwing include windup, early cocking, late cocking, early acceleration, late acceleration, deceleration, and follow-through.
Pitcher throw a variety of pitches, each of which has a slightly different velocity, trajectory, movement, hand position, wrist position and/or arm angle.
Effective pitching is vitally important to a baseball team, as pitching is the key for the defensive team to retire batters and to preventing runners from getting on base. A full game usually involves over one hundred pitches thrown by each team. Multiple pitchers are often needed in a single game, including the starting pitcher and relief pitcher(s). The rules do not limit the number of pitchers that can be used in a game; the only limiting factor is the size of the squad, naturally.