sack up v. to become bold, courageous, or forthright; to nut up, man up. (source: Double-Tongued Dictionary)
Further reading
If there’s a logophile on your gift list, you have lots of choices, including a new trivia game for language-lovers and a murder mystery for the word-obsessed. Plus, if someone calls you a schmoozer, should you be flattered or insulted? And if...
A Green Bay Packers fan wonders why a quarterback who’s tackled is said to be sacked. The roots of the word sack as in “bag” goes back thousands of years, all the way to Akkadian, later spreading through Greek, Latin, and then to Romance and...