This word meaning to mock or jeer an opponent, especially in a sporting context, dates from the late 19th century. Although there is still some controversy as to the exact origin of this word, it seems safest to agree with the OED that it derives from one of the Australian aboriginal languages, where borak means to make fun. This was then anglicised into barrack. Not everyone agrees. Eric Partridge in his Dictionary of Slang and Unconventional Usage favours the theory that it comes from cockney slang barrikin meaning a jumble of words or gibberish. Most people believe that the Australians, if they did not invent barracking, certainly perfected it. On that basis alone, it seems wise to agree with the OED on the Australian origin.