“In 1957, Army felt very confident of beating Navy on the basis of two pieces of information which, at first notice, might seem inconsequential. From scouting and the study of movies, Army could tell the direction of the slant of the Navy line by the position of the heel of the defensive tackle. If the tackle’s heel was up off the ground, he and the rest of the internal linemen were going to slant to the defense’s right. If the heel was down, the slant would be in the opposite direction.”