Throw Down the Gauntlet

A gauntlet, from the French gantelet, was the reinforced armoured glove worn by medieval knights, and throwing one down at another knight's feet was a formal, deliberately public way of challenging them to a duel or trial by combat. Picking the glove up meant accepting the fight; leaving it on the ground meant refusing, and risking being branded a coward. The figurative sense, issuing a bold challenge in an argument, a competition, or anything else, is recorded from the second half of the 1700s. It's easy to confuse this with the completely unrelated "running the gauntlet," a brutal military punishment where a man was made to run between two lines of soldiers striking him; the two phrases share the word "gauntlet" purely by coincidence, not by shared origin.