NA as a major league

Whether to cover the National Association of Professional Base Ball Players (1871–1875) as a major league is a recurring matter of difference in historical work on American baseball among historians, encyclopedists, database builders, and others who work on the facts of baseball history on the playing field.

The National Association of Professional Base Ball Players was the first professional baseball organization. It operated from 1871 until 1875. Whether to treat it as a major league has been a contentious issue in baseball historiography and statistics, because the major leagues utterly dominate not only publication but thinking, talking, and writing about the history of the game on the field. The careers of players and field managers as participants, of clubs, and even cities, as competitors are all viewed through the prism of what was accomplished during their major league careers.

For example, it is routine to say that a player's career began when he first appeared in a major league game. Players retire from baseball when they last appeared in a major league game. A player will have "played baseball for two seasons" if he appeared in major league games during two calendar years — whether he played two games in emergencies, recruited from the fans in attendance, or two full seasons during a professional career of twenty years.

The abbreviation "NA" (rather than "NAPBBP") is common today. Even in formal prose, where it is often used in parentheses to make a proper noun such as "Boston (NA)". As such it specifies one baseball club among all those with names that have the natural short form "Boston", such as "Boston Base Ball Club, Incorporated".

The importance of and widespread familiarity with two-letter abbreviations for baseball leagues is related to the publication of encyclopedic works, in print since the 1950s and on the web in the 21st century, whose main feature is historical playing records of baseball seasons. Leagues govern seasons, annual competitions with their own championships at stake, if nothing else. Leagues publish playing records for the participants in their league seasons. So league seasons have become the basic unit of baseball's historical record as it is widely disseminated; game records are retained by league offices or deposited in archives such as the Baseball Hall of Fame collections, when not lost in fires. The playing records portion of a baseball reference work is full of entries for individual players that consist mainly of long lines of numbers prefixed by something like "Bos NA 1871", specifying one club in one league-season. All of the (candidate) major leagues in baseball have standardized two-letter abbreviations such as NA — namely, NA, NL, AA, UA, PL, AL, FL — whose crucial value is in this encyclopedic context.

...
Wikipedia