A person who jeeringly criticizes or heckles performers, speakers, or athletes, or someone who shouts encouragement at sporting events.
From 'barrack' (to jeer) plus the agent noun suffix '-er' (one who does). The term developed primarily in Australian English slang during the 19th century, becoming mainstream in sports vocabulary.
Professional sports teams and promoters started paying 'barracker' groups to jeer opposing teams—this became organized fan behavior, showing how what started as crowd rudeness became a legitimate (if controversial) part of the sports entertainment business.
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