For my money, the defensive spectrum ranks among the most useful concepts James introduced during his Baseball Abstract days. Cobbling together from various Abstracts, James defined the spectrum—DH-1B-LF-RF-3B-CF-2B-SS—as an "an arrangement of defensive positions according to raw abilities needed to learn to play each," with "speed, agility, reaction time, and throwing" the primary ones. His key observation was that offensive ability increases the further left a position sits on the spectrum, due to the selective pressure applied to the talent pool, while defensive ability increases the further to the right a position sits. It's much easier to find players who can hit well while filling the less defensively demanding positions, an observation that has an intuitive appeal for the casual fan, for it explains the seemingly endless supply of big galoots who can mash but wear iron gloves, as well as flyweight middle infielders who can pick it but can't hit their weight.