To deliver into the hands of an enemy
play false, break faith (with), inform on, inform against, turn in, commit treason, turn informer, delude, break one's promise, be false to, be false-hearted to, be disloyal to, go over to the enemy, trick, let down, disappoint, deceive, sell down the river*, play Judas*, give the Judas kiss to*, double-cross*, deliver up*, sell out*, stab in the back*, bite the hand that feeds one*, cross up*, turn state's evidence; see also deceive, inform 2.
Antonyms support*, adhere, stand firm.