Gauntlet has two meanings. Firstly a gauntlet is a kind of heavy protective glove, originally a piece of armor and now often used as protective clothing by welders and other workers. The gauntlet was also a type of challenge in Native Indian culture. Men would line up in two straight rows, often with mild weapons like switches, and a single man would run down the middle. This practice fell out of favor as barbaric, having led to many deaths.
To "throw down the gauntlet," or "fling down the gauntlet" is an idiomatic expression that means to issue a challenge. It comes from a Medieval European method of challenging someone to a duel; the challenger would drop a gauntlet (later a glove) and the other person could accept the challenge by picking it up.