1996 - The Strike Zone is expanded on the lower end, moving from the top of the knees to the bottom of the knees.

1988 - "The Strike Zone is that area over home plate the upper limit of which is a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants, and the lower level is a line at the top of the knees. The Strike Zone shall be determined from the batter's stance as the batter is prepared to swing at a pitched ball."

1969 - "The Strike Zone is that space over home plate which is between the batter's armpits and the top of his knees when he assumes a natural stance. The umpire shall determine the Strike Zone according to the batter's usual stance when he swings at a pitch."

1963 - "The Strike Zone is that space over home plate which is between the top of the batter's shoulders and his knees when he assumes his natural stance. The umpire shall determine the Strike Zone according to the batter's usual stance when he swings at a pitch."

1957 - "A strike is a legal pitch when so called by the umpire which (a) is struck at by the batter and is missed; (b) enters the Strike Zone in flight and is not struck at; (c) is fouled by the batter when he has less than two strikes at it; (d) is bunted foul; (e) touches the batter as he strikes at it; (f) touches the batter in flight in the Strike Zone; or (g) becomes a foul tip. Note: (f) was added to the former rule and definition."

1950 - "The Strike Zone is that space over home plate which is between the batter's armpits and the top of his knees when he assumes his natural stance."

1910 - "With the bases unoccupied, any ball delivered by the pitcher while either foot is not in contact with the pitcher's plate shall be called a ball by the umpire."

1907 - "A fairly delivered ball is a ball pitched or thrown to the bat by the pitcher while standing in his position and facing the batsman that passes over any portion of the home base, before touching the ground, not lower than the batsman's knee, nor higher than his shoulder. For every such fairly delivered ball, the umpire shall call one strike."

"An unfairly delivered ball is a ball delivered to the bat by the pitcher while standing in his position and facing the batsman that does not pass over any portion of the home base between the batsman's shoulder and knees, or that touches the ground before passing home base, unless struck at by the batsman. For every unfairly delivered ball the umpire shall call one ball."

1901 - "A foul hit ball not caught on the fly is a strike unless two strikes have already been called." (NOTE: Adopted by National League in 1901; American League in 1903).

1899 - "A foul tip by the batter, caught by the catcher while standing within the lines of his position is a strike."

1894 - "A strike is called when the batter makes a foul hit, other than a foul tip, while attempting a bunt hit that falls or rolls upon foul ground between home base and first or third bases."

1887 - "The batter can no longer call for a 'high' or 'low' pitch."

"A (strike) is defined as a pitch that 'passes over home plate not lower than the batsman's knee, nor higher than his shoulders.'"

1876 - "The batsman, on taking his position, must call for a 'high,' 'low,' or 'fair' pitch, and the umpire shall notify the pitcher to deliver the ball as required; such a call cannot be changed after the first pitch is delivered."

High - pitches over the plate between the batter's waist and shoulders

Low - pitches over the plate between the batter's waist and at least one foot from the ground.

Fair - pitches over the plate between the batter's shoulders and at least one foot from the ground.