If people in an audience barrack public speakers or performers, they interrupt them, for example by making rude remarks. To bother or interrupt (someone, such as a performer or speaker) by shouting comments or criticism; To shout in support of a person or group often + for

A building or group of buildings for lodging soldiers, especially in garrison. See examples of barrack used in a sentence. Phrasal verb barrack for someone (definition of barrack from the cambridge advanced learner's dictionary & thesaurus © cambridge university press)