Why is K the letter used for a strikeout?

There are two theories as to how “K” came to stand for strikeout. Henry Chadwick, who invented a scoring system in 1861, developed a series of letter symbols, choosing “K” for strikeout. He explained, “It was the prominent letter of the word ‘strike,’ as far as remembering the word was concerned.” A second story gives M.J. Kelly of the New York Herald credit for inventing the symbol.