Related Post: MLB Ejection 105: Tim Timmons (5; David Ortiz) (7/28/13).
Related Post: Determining The League's Biggest Hothead (It's Big Papi) (6/11/15).
We recall that the vertical strike zone falls between "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 hollow beneath the kneecap."
It is determined from "the batter’s stance as the batter is prepared to swing at a pitched ball."
There is debate as to what this actually means, as in when exactly *the moment* occurs when the stance height shall be taken—or if it remains variable throughout the entire pitch sequence up until the pitch's arrival at home plate.
As far as the spirit and history of the rule is concerned, consider that in 1963, the strike zone's time-of-capture was changed from the preceding, "when [the batter] assumes his natural stance" to "The umpire shall determine the Strike Zone according to the batter's usual stance when he swings at a pitch." In 1988, we arrived at the modern "prepared to swing at a pitched ball" phrasing (1988 also changed the upper boundary of the zone, or as NL umpire supervisor Ed Vargo once said, "the nipple line, but they didn't want to put 'nipple line' in the rule book"). In 1996, the zone's lower limit moved from the top of the knees to the bottom (hollow) of the knees.
The effective natural-stance to prepared-to-swing change is rather rudimentary.
Natural Stance (Obsolete/Old Rule): A batter's "natural stance" is generally a consistent crouch regardless of the pitch and requires the umpire to calculate where this "natural stance" exists for each pitch, regardless of where the batter physically stands when the baseball gets to home plate. For example, a batter squaring to bunt rarely is in "his natural stance," which could theoretically make pitch-calling complicated (and somewhat nonsensical). The "natural stance" principle is used in most modern computerized pitch tracking applications (which is another reason why the computers are deficient). Finally, 1969's "as he swings"—which serves as the basis for capture (implicitly, this means the umpire should judge the zone as the pitch is actually crossing home plate)—has one glaring error: the batter can't possibly swing at any callable pitches, for by swinging, the pitches are no longer callable (e.g., a swing takes away the ball vs. called strike judgment call).
Prepared to Swing (Modern Rule): By removing the "natural stance" and "as he swings" terminology, the umpire is now free to call the strike zone relative to the batter's actual physical position as the pitch arrives, with no implication of an actual swing (though, again, this complicates bunt attempts and situations, like Ortiz's, when the batter gives up on the pitch). Both "natural stance" and "prepared to swing" are designed to prevent batters from doing things like deliberately ducking to the ground in order to minimize their strike zone height, but only "prepared to swing" allows the umpire to make modifications on the fly that may deviate from the static image conjured up by a "natural stance."
Conclusion: Umpires should bear in mind that a strike zone's lower and upper limits are never truly finalized until the pitch arrives at home plate. Common sense and fair play principles should dictate how to adjudicate the strike zone when the batter is on the move, with greater consideration reserved for ensuring the batter isn't trying to "game" the system by deliberately ducking or jumping away from a pitch that would otherwise be ruled a strike.
Wrap: Argentina vs. Colombia (Serie Latinoamericana), 1/28/19 | Video as follows:
