1. adj. — Sports, informal, slang
of or pertaining to an informal sporting event.
Scrub is an adjective designating an informal sporting event. The nominal form of scrub is thought to have first meant “a low stunted tree” (OED-3, s.v. “scrub” (n.1)) with citations appearing as early as the 14th century. Over time, the meaning branched out and became associated with other “small” or “poor/lowly” entities (i.e. livestock, humans). In modern American and British varieties of English, the term scrub has many connotations of inferiority or amateurism and is used in relation to anything from plant quality to sports. EDD (s.v. “scrub” (4, 6)) offers “an inferior quality of teazle” or “a low, worthless fellow” as some definitions of the term.
However, American sources are also well documented with long pedigrees. DAE (s.v. "scrub" (a.3)) narrows its meanings to the context of sports, describing an example of the attributive use of scrub as “scrub team - an athletic team, as in football, made up of players inferior to those on the 'first' team”. This is precisely the present meaning. OED-3 (s.v. “scrub” (a.4)) reiterates this American focus on non-professional sports or team members, stating "of a team or player: not first-class, not of regular standing; of a game: played by scrub or scratch teams".
Though COD-2 (s.v. “scrub” (4b)) marks the noun scrub in the sports context as “Cdn”, DAE offers citations dating back to 1868, antedating the earliest Canadian citation (see below). Canadian usage differs from American English usage only in that it is occasionally applied to casual hockey games (see the 1962 and 2016 quotations) and not simply to baseball or football. This, however, is due to a historical focus on different kinds of sports in these countries, a difference that has been watered down since the 1960s. Scrub hockey has traditionally been called shinny (meaning 1b).
See also: shinny (meaning 1b)
2. n. — Sports, informal, slang
an informal sports match.
See meaning 1.
See also COD-2, s.v. "scrub" (2.4b), which is marked "Cdn."