by UmpSteve » Mon May 30, 2011 1:39 pm
Real world answer:
If a pitcher places her foot (either foot!!) where it contacts the pitcher's PLATE as required by rule, then her subsequent movements do not advance the pivot foot to a place where it would not remain in contact if kept flat to the surface, nor slide back the nonpivot foot to a place where it would not remain in contact if kept flat to the surface, then the pitcher has realistically met the requirements of the rule.
The pitching rules exist to make the pitchers pitch from the same location on the field, the same distance, and with the same requirements and limitations. Raising a heel or toe so that it partially clears the ground without actually moving the foot isn't (and shouldn't be) a violation. That simply doesn't meet the purpose for the pitching rules; it isn't to micromanage and find innovative ways to create illegal pitch calls, it is to force all pitchers to meet certain minimum requirements while not gaining an unintended advantage.
That is the same interpretation and rule determination that allows a foot to slide across the pitcher's PLATE without violation, to clear the cleats to keep from getting caught while sliding, and yes, to use a slide step forward with the pivot foot so long as the stopping point is still above the plane of the pitcher's PLATE. True in all directions, and in all rule sets.