The problem, sources said, stems from technological leaps that caused unintended consequences. In 1996, when the league last changed the strike zone to extend it from the top of the knees to the bottom, beneath the hollow of the kneecap, it did so to encourage umpires to call knee-level strikes. The lower end of the zone, in practice, was about three-quarters of the way down the thigh, so the idea was that by adjusting the eye levels of umpires to look lower, the result would be a more traditional strike zone.
Then along came Questec, the computerized pitch-tracking system, followed by Zone Evaluation, the current version tied in to MLB’s PITCHf/x system. With a tremendous degree of accuracy – especially in recent years – the systems tracked textbook balls and strikes, and the home-plate umpires’ performances were graded on a nightly basis. Over time, not only did umpires’ strike zones move down to the knees, they went to the hollow and even a smidge below.
“I don’t think the Playing Rules Committee at the time of the last change ever expected that the umpires would call strikes at the hollow of the knee,” said Mets general manager Sandy Alderson, the current chairman of the committee. “To their credit, the umpires now are.”