In baseball, the strike zone is the space directly above home plate through which a pitch must pass in order to be recorded as a strike. The official strike zone is defined horizontally as the space between the outside edges of home plate and vertically between the spot just below the kneecaps and the midway point between the shoulders and the waistline of the batter.
Although the strike zone is strictly defined as the same space in all baseball games, balls and strikes are called by the home plate umpire. This causes strike zones to vary, depending on the umpire behind the plate. Some umpires favor a lower strike zone, often calling pitches below the knees a strike, while others will favor a higher strike zone. The same can be said for pitches on the inside or outside portion of the strike zone. A pitch that touches or is slightly outside the border of the strike zone (called a "borderline pitch") is referred to as a "pitcher's pitch", as the pitch is often called a strike, even though it may appear to the batter or other players to be a ball. Catchers will also attempt to manipulate the strike zone favorably by moving their mitt closer to the strike zone upon catching a pitch.