put up one's dukes

Meanings

1. 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.
2. To take firm action or to show oneself to be committed to such action, as when competing in a sporting event or other contest.

Etymology

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. Another possibility is Cockney rhyming slang as explained at duke. It could also be a convoluted--though erroneous--reference to the 9th Marquess of Queensberry (after whom the rules for modern boxing were initially named).