What is the origin of the word "whitewash" in the context of sports?

Solution 1:

There's nothing racist about it. The figurative use comes from the literal use of applying a kind of white paint to walls, from the 16th century as a verb. This was then used figuratively to mean to cover up faults, blemishes, or otherwise give a fair appearance (18th century as a verb).

The sporting use is applied when the loser fails to score, or loses all the games in a series, or more loosely is beaten by a large margin, and comes from baseball. The OED's first citations for the noun and the verb are both 1867:

1867 Chicago Republican 6 July 2/6 The Unions were whitewashed 3 times, and the Forest Citys 5 times.

1867 N.Y. Clipper 31 Aug. 164/2 The first ‘whitewash’ of the [baseball] game was drawn by the Mutuals.

In the verb case, it says the beaten team were whitewashed. This is analogous to their part of the scoreboard remaining clean and blank.

I found an antedating from the year before in the Cleveland Daily Leader, June 18, 1866, Morning Edition, "Baseball":

The fifth and sixth innings resulted favorably to Cleveland. The seventh was a whitewash for both clubs. The eighth, which was by mutual agreement the last, added seven to the score of each, and the final result stood: Forest City, 40; Reserve 26.

Solution 2:

Etymonline does not mention the use of whitewash in sport. But it is still interesting as the modern use is derived from these senses:

1590s, "to wash a building surface with white liquid," from white + wash. Figurative sense of "to cover up, conceal" is attested from 1762. Related: Whitewashed; whitewashing. The noun is recorded from 1690s.

Wiktionary and a couple of other places date the sporting sense of the term to baseball from the 1800s:

(baseball, slang, dated, late, 19th century, archaic) To prevent a team from scoring any runs.

In his book, High and inside: an A to Z guide to the language of baseball (1997), Joseph McBride notes:

To "whitewash" a team, a term that can be traced back as far as 1851, is to obliterate it, just as whitewash does to the previous coloring of a fence. The word used today is "shutout." Synonyms for "whitewash" were "kalsomine" and "calcimine," ...

_{^{Considering the fact that the first official baseball game is said to have taken place in 1846, this is remarkable.}}

So it appears that there are no racist undertones to the term. That said, for reasons unknown, it has fallen out of fashion in baseball and has been replaced by the term shutout.

Whitewash is still in widespread use in other sports, most notably, cricket. While I wouldn't consider the following to be racist, it is still noteworthy:

West Indies' consecutive 5–0 defeats of England in 1984 and 1985-86. These two results are also commonly labelled blackwashes because of the dark skin of the West Indies players.

Also of passing interest:

Whitewashed is a term used to describe a member of a racial minority group, often those of Asian heritage, who have culturally assimilated to white, Western culture. Whitewashed individuals know little of their native culture. The term is typically used in a derogatory manner. It's akin to calling someone a racial sellout.

Solution 3:

I don't think whitewash could be racist. It is like someone having worked hard to make a painting and later you whitewash it, so you have destroyed the hours of effort and hard work it took to make the painting, back to zero.

So in sports whitewash is that you don't let the effort of opponents bear fruit, score remains zero despite their full efforts, you have ruined the entire hard work they put in for the game, preparation etc. so you have whitewashed your opponents.