From Alan Schwarz’s The Numbers Game: Baseball’s Lifelong Fascination with Statistics:

To spread the gospel, Chadwick invented his own personal scoring form in the hope that it would become standard. The grid extended nine players deep and nine innings wide, each box housing a player’s at-bat as he came up in turn. Each outcome was coded with either numbers, for the fielder who handled the ball, or letters, to denote a fly ball or the like. (Many of those letters were chosen as the last of the events they connoted, such as “D” for catch on bound, “L” for fouball and “K” for struck out, the last of which has survived to delight generations of kids as they first learn to score.)

The thing about the scoresheet, as I learned to do it (part from my Mom and part from my friend Jim Timmermann) is the way two things stand out in a glance at the complex hieroglyphics – the runs scored and the big bold K’s. Obviously at the end of the day it is the former that matter. But I love good pitching, so I like it that the latter also stand out in a tradition dating to Henry Chadwick in the 1850s.

And no, “K” doesn’t stand for Koufax.

When he wrote his name in capital letters in the record books, that “K” stands out even more than the O-U-F-A-X.