redshirt v. to hold a child back for an extra year before admittance into kindergarten. Etymological Note: From sports, where “red-shirting” is holding a player back for an extra season or semester in order to maximize his or her total years of eligibility, to increase skills or maturity, or to otherwise improve suitability for a team or roster. In that context, the term dates to at least as early as 1950. (source: Double-Tongued Dictionary)
Further reading
juicy noun. A person who illicitly carries alcohol in a water bottle. «Gwen Alexander, who’s been working at the Astoria pool for two years, confirms there haven’t been any issues with fighting this year but she said rule enforcement is...
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Not being a sports fan, I’d never heard of this one. I am familiar with the Star Trek derived Red Shirt…otherwise known as the Expendable Crewmember who gets killed early in the episode.
The Star Trek “red-shirt” is completely unrelated.