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)
- 1889  He would talk on anything, but when we broached our favorite topic [of baseball], he became an oyster, tout de suite. Arrived in Ottawa, we tried to have him play, but he said he was tired, so we had to await his pleasure. At last, after much coaxing, he consented to play short stop in a scrub game. 
- 1899  "I have been told," said the football player to his fiancee, "that you have been engaged before; that I am not the first[.]"
The intensity of his passion made her shudder, but she quickly recovered herself.
"And is it not proper," she demanded, "before playing a match game to try a few practice games with scrub teams?" 
- 1921  During these many weeks of silence, the senior team has continued systematic practice and a general transformation has taken place; in fact the team has been so reorganized and revised that it is scarcely recognizable. A try out with a scrub team last week proved the new arrangement most efficient. 
- 1962  Skating enthusiasts skated to the music of Joe Szemes' orchestra and a game of scrub hockey was in full swing. If the ice lasts long enough down on ye ole swimming hole maybe we will be able to see a hockey game this weekend. 
- 1985  A siren means you go straight home no matter how well you're playing in a scrub softball game. 
- 2000  "They will be placed in groups of eight or less and coaches will teach them the basics of throwing, catching and hitting," he said.
"They will also get to play mini-games or scrub games. We'd like the kids to play four-against-four so they get involved in the games." 
- 2008  Following the story portion of the itinerary, games and activities will be available including scrub baseball, netball, horseshoes, street hockey, bocce ball and a special scavenger hunt for the small children. 
- 2016  Schedule for Adult Scrub Hockey
Description: For players 18 years and up. A fun, recreational drop-in hockey session. Non-contact. Full hockey gear is required. 
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."
- 1984  As a saleswoman for a Toronto book company, she misses many of the games when on the road, but she still plays as often as she can. While on a sales call at a Windsor bookstore she overheard the owners talking about their pick-up game that evening and invited herself along. She has even disguised herself as a young man to play in "all male" shinny games in her neighborhood. Ms Brickman played organized hockey in women's leagues and at the University of Manitoba, but shinny, or "scrub," as she calls it, is her favorite.
Ms Brickman's history of hockey playing is exceptional. The joys of hockey playing are not part of every woman's childhood as they are for most men. 
- 1996  Yesterday morning at Maple Leaf Gardens, after the Chicago Blackhawks had a brisk, half-hour pre-game skate, three scrubs, two coaches, a backup goaltender and an injured regular stayed on the ice for extra drills and an impromptu game of three-on-three. The audience for a National Hockey League game is measured by thousands, for a practice by dozens, and for scrub workouts with the fingers on one hand. By the time these Black Aces started their pickup game, the audience had dwindled to two, the Zamboni driver and your correspondent. 
- 2002  Am I the only one who recalls from the spring of his seventh or eighth year an introduction to a perpetual form of baseball called scrub? As soon as the diamonds were dry enough for rubber boots, we'd be out there playing, boys and girls of all ages. In scrub, a lad started as a deep fielder, and with each out progressed to positions closer to the plate until he had his turn at bat, and then over and over, until it was time to leave home for work or college. Whatever became of scrub, I have no idea, unless it's now some sort of computer game, Scrubmania 2002 or something, featuring radioactive lizards that apply martial-arts style flying kicks to the catcher's head when sliding home, in which case I would not be surprised. 
- 2009  In the summer, I'd head to the park with my baseball glove, or my football or soccer ball - or all three - to meet up with my friends. If we didn't have enough kids for a real baseball game, we'd play scrub or .500, or practise rundowns. 
- 2013  And I love all of my grandchildren, even though they eyed me with suspicion when later that morning I suggested we play scrub. The suspicion was fueled by a generation gap wider than the Grand Canyon and kept alive by a new language spoken by these mysterious devices the kids carry with them always. I'm convinced they carry those things so they don't have to carry on real, live conversations with people like grandmas.