A player’s batting average is determined by dividing his total number of hits by his total times at bat. The number is taken to three decimal places. This has long been the main measurement of a player’s offensive output, but Bill James argued that it was overvalued. The goal of a team was to score runs, not make hits per se. Hits score runs, but so do walks, a figure that was largely ignored. Thus, James thought that on-base percentage (see below) should be used instead of batting average as a more accurate evaluation.

The baseball box score was invented in 1845 and revised 14 years later by Henry Chadwick. It summarizes an individual game’s statistics, both those of the teams and specific players. Lewis writes that Chadwick, who was British, saw the game too much through the lens of cricket and devised his statistics accordingly. He also created statistics for those things that were easiest to count, not necessarily things that matter the most. In the 1970s, Bill James argued that Chadwick’s statistics, which had changed little over the decades, were inaccurate and in some cases useless to determining a team’s or player’s actual value.