Strike zone boundaries (MLB)
Definition In baseball, the strike zone is a conceptual rectangular area over home plate which defines the boundaries through which a pitch must pass in order to count as a strike when the batter does not swing. The top of the strike zone is the mid-level between the top of the batter's shoulders and his belt, and the bottom is at the level just beneath the knee cap. The right and left boundaries of the strike zone correspond to the edges of home plate. A pitch at which the batter does not swing and which does not pass through the strike zone is called a ball.
A batter who accumulates three strikes in a single batting appearance has struck out and is ruled out; a batter who accumulates four balls in a single appearance has drawn a base on balls (or "walk") and is awarded first base. In very early iterations of the rules during the 19th century, it took up to 9 balls for a batter to earn a walk; however, to make up for this, the batter could request the ball to be pitched high, low, or medium.
Technically, the strike zone has depth as well; the rules define a volume of 3-dimensional space – a right pentagonal prism. If any part of the ball touches any part of this space, it is a strike. For most practical purposes, though, the depth of the zone is irrelevant.
Enforcement While baseball rules provide a precise definition for the strike zone, in practice it is up to the judgment of the umpire to decide whether the pitch passed through the zone. Umpires often call pitches according to a contemporary understanding of the strike zone rather than the official rulebook definition. The conventional definition that prevails in Major League Baseball shifts the whole strike zone laterally a few inches away from the batter while truncating the zone vertically near the batter's belt.
In 2001, Major League Baseball directed its umpires to call pitches according to the official definition rather than the conventional one. Umpires were to call "high" strikes and "inside" strikes, while pitches just off the outside part of the plate were to be called balls. The umpires demonstrated limited compliance for a time, but before long the de facto strike zone had returned to the conventional definition.
Many factors have contributed to the divergence of the official and conventional strike zones. Changes began in the 1970s, when umpires upgraded their chest protection in favor of more compact vests allowing them more movement. Crouching lower meant lowering their line of vision, and caused the boundaries of the strike zone to sink lower. As pitchers lost the higher strike zone, they began throwing lower and to the outside, which caused hitters to move closer inside.
At the same time, there was a shift in attitude among both players and league officials regarding pitches thrown inside. While pitchers of the 1960's like Bob Gibson regarded it a pitcher's right to throw high and inside, later batters were more likely to take offense at such treatment. Major League Baseball also tightened its rules prohibiting pitchers from intentionally hitting batters, removing the warning pitchers formerly received before being ejected from a game. The inside pitch was largely taken away from the pitchers, which freed hitters to move closer to the plate and look for the ball outside.
Despite the fact that the conventional strike zone is a departure from one of the fundamental rules of baseball, the difference does not garner a great deal of attention. Players, managers, and umpires alike consider consistency rather than accuracy to be the most important characteristic of an umpire's effective strike zone.
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