The perspicacious perfectionist mapped his hits down to the percentage point
In 1968 Ted Williams and SI senior editor John Underwood wrote a five-part series for this magazine, which became the basis for the 1969 book My Turn at Bat. In the fifth installment, "Science of Batting," Underwood introduced Williams's chart (above) of the hitting zone with the accompanying text.
... Williams' first rule of hitting was to get a good ball to hit. He learned down to percentage points where those good balls were. The box shows his particular preferences, from what he considered his "happy zone"—where he could hit .400 or better—to the low outside corner—where the most he could hope to bat was .230. Only when the situation demands it, says Williams, should a hitter go for the low-percentage pitch. Since some players are better high-ball hitters than low-ball hitters, or better outside than in, each batter should work out his own set of percentages. But more important, each should learn the strike zone, because once pitchers find a batter is going to swing at bad pitches he will get nothing else. The strike Zone is approximately seven balls wide (allowing for pitches on the corners). When a batter starts swinging at pitches just two inches out of that zone (shaded area), he has increased the pitchers target from approximately 4� square feet to about 5[5/6] square feet—an increase of 37%. Allow a pitcher that much of an advantage, says Williams, and you will be a .250 hitter.