knuckle up
verb1
Informal To clench one's fist(s) as though in preparation for a fight.
Chiefly African-American Vernacular
- With a resolve to get his son away from these monsters, Isaac knuckled up and mean-mugged his opponent.2012, Vanessa Miller, Latter Rain:
- Tony stumbled a little and when he found his balance, he knuckled up and sent a jab toward Will's neck.2012, Pink Maxwell, A Scorpion's Sting, page 209:
2
Broadly, Informal To approach a problem aggressively.
3
Slang To strike or fight.