Strike Zone

Definition

The official strike zone is the area over home plate from the midpoint between a batter's shoulders and the top of the uniform pants -- when the batter is in his stance and prepared to swing at a pitched ball -- and a point just below the kneecap. In order to get a strike call, part of the ball must cross over part of home plate while in the aforementioned area.

Strikes and balls are called by the home-plate umpire after every pitch has passed the batter, unless the batter makes contact with the baseball (in which case the pitch is automatically a strike).

History of the rule

The vertical specifications of the strike zone have been altered several times during the history of baseball, with the current version being implemented in 1996.

Past strike zones

From 1988-95, the strike zone went from the midpoint between the shoulders and the top of the uniform pants, to the top of the knees.
From 1969-87, the strike zone went from the batter's armpits to the top of the knees. This strike zone was implemented, along with the lowering of the mound from 15 inches to 10 inches, in response to a 1968 season -- now known as the "Year of the Pitcher" -- in which the dominance of hurlers reached new heights.
From 1963-68, the strike zone went from the top of the batter's shoulders to the knees.
From 1950-62, the strike zone went from the batter's armpits to the top of the knees.
The version of the strike zone used from 1963-68 was also utilized prior to 1950, going back to the late 1800s.

Note: The box outlined above delineates the borders of the Major League strike zone.