mail it in
v. phr.— «Experienced horses may cheat or protect themselves during a race (in human sports vernacular they are “mailing it in”).» —by John Lindley Handicapping for Bettor Or Worse Apr. 25, 2004. (source: Double-Tongued Dictionary)
Further reading
What if, instead of being an inanimate object, a dictionary were alive? That’s the idea behind a lavishly illustrated new children’s book called The Dictionary Story (Bookshop|Amazon) by Oliver Jeffers and Sam Winston. This is part of a...
Jim in Columbia, South Carolina, has noticed sportscasters’ use of the phrase on the season with reference to a period of time. This construction shows up in the sports pages as early as the 1880s, first referring to a team’s revenue and...