HIS NEW GLOVE is jet black, with gold stitching. From afar, it looks like any other mitt, but up close, it is unlike any glove you've seen. It has six fingers, or four fingers and two thumbs, with a small nest of a pocket in its middle, splitting the half-dozen digits precisely in half. It looks made less for a hand and more for a paw. The man can remember the first time he held a six-fingered glove. He was 7 years old. His father had searched for one that could accommodate the skills of his special boy, and he discovered that Mizuno in Osaka, Japan, had made one. In 1995, a man with a mustache had pitched a...