During its earliest years, professional baseball was

During earliest years professional baseball was known as "Rounders".

Explanation:

The term baseball can be dated to 1744 in John Newbery's children's book A Nice Little Pocket Book. The book contains a short poem and an illustration depicting a game called baseball. Interestingly, the basics of the illustration are marked with posts instead of the pockets and flat plate that are now so well known in the game. The book was popular in England and was reprinted in North America in 1762 (New York) and 1787 (Massachusetts).

Many other early references to racket and ball games with bases are known: a British newspaper from 1749 referring to Frederick Louis, Prince of Wales, who plays "bass ball" in Surrey, England; "Play on the Base" at the American Army camp in Valley Forge in 1778; the ban on students "playing with balls and sticks" at the Commons of Princeton College in 1787; a note in the memories of Thurlow Weed, a publisher and politician from northern New York, of a baseball club founded around 1825; a newspaper report that the Rochester Baseball Club (New York) had about 50 members in the 1820s; and remembers old Oliver Wendell Holmes about his days at Harvard in the late 1820s and said he played a lot in college.

The Boy's Own Book (1828), and often frequently reprinted book on English sports played by children of that time, contained a chapter on rounders play in its second edition.

I am 75 % sure it's the first one

Explanation:

it has four categories