from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To raise one's clenched fists in front of one's body and stand in a threatening or defiant manner, in preparation for a fistfight.
- v. To take firm action or to show oneself to be committed to such action, as when competing in a sporting event or other contest.
Possibly by analogy to a king or other ruler summoning his dukes, and by extension the duke's knights or other soldiers, to battle an enemy. Or possibly Cockney rhyming slang (see duke). (Wiktionary)