1. Throw down the gauntlet
Meaning : To issue a challenge .
A gauntlet-wearing knight would challenge a fellow knight or enemy to a duel by throwing one of his gauntlets on the ground. The opponent would pick up the gauntlet to accept the challenge.
2. To eat humble pie
Meaning : To apologize and face humiliation for a serious error.
3. Hand in glove
Meaning : if one person or organization is working hand in glove with another, they are working together, often to do something dishonest
E.g. It was rumoured at the time that some of the gangs were working hand in glove with the police.