Step right up and listen here! Ballyhoo is slang for the attention-getting talk or performance by a circus or carnival barker that is intended to lure passersby to a show.
He'd worked himself up a stunt of sticking a trick knife through one arm to attract a crowd and then starting his ballyhoo ...
— Fred Gipson, Fabulous Empire, 1946
This sense of ballyhoo is first recorded in print in the beginning of the 20th century and, soon after, was extended to exaggerated or sensational promotion or publicity of any kind.
Can Cooney take a punch? Can he go the distance? They wonder. They say he has never been tested, and about this they are probably right. Naturally, Gerry has snappy counters to their jabs. ... But mostly he is wry of the whole prefight ballyhoo.
— William Plummer, People, 14 June 1982