1
general::
Declare or issue a challenge, as in The senator threw down the gauntlet on the abortion issue. This expression alludes to the medieval practice of a knight throwing down his gauntlet, or metal glove, as a challenge to combat. Its figurative use dates from the second half of the 1700s, as does the less frequently heard take up the gauntlet, for accepting a challenge.
American Heritage Idioms
2
general::
Phrase(s): throw down the gauntlet
Fig. to challenge someone to an argument or to (figurative) combat. • When Bob challenged my conclusions, he threw down the gauntlet. I was ready for an argument. • Frowning at Bob is the same as throwing down the gauntlet. He loves to get into a fight about something.
McGrawhill's American Idioms And Phrasal Verbs