MECCA Arena (1979). The New Barbarians fronted by Ron Wood included Keith Richards, Stanley Clarke on bass and Bobby Keys on saxophone. For months there was speculation on who was to be their special guest(s). Mick Jagger? Mick Taylor? Jeff Beck? Eric Clapton? When the band completed the encore and the lights came up, it became apparent there wasn't a special guest. A riot broke out on the arena floor. People were throwing chairs, throwing bottles, fighting - I grabbed my girlfriend's hand and led her up the stairs to the topmost exits.
Harley Davidson 100th Anniversary (2003). For months there was speculation on who the top secret surprise headliner at the free concert would be. The Rolling Stones? Aerosmith? Several metal bands (Motorhead?) which would appeal to bikers? Nope. Elton "Candle In The Wind" John walked out on stage. "I'd sing you a song about motorcycles but I don't know any." No riot. The capacity crowd quickly left, kind of like the Shaggy to Surly exodus.
Electric Ballroom (1981). Wendy O Williams of the Plasmatics arrested onstage while simulating sex with a sledgehammer. Near riot as a dozen audience members were arrested for throwing things at the police.
Summerfest (1972). George Carlin arrested for saying The Seven Words You Can't Say On TV. Carlin's career was not doing well as he shifted from a short-haired "square" doing his Hippy Dippy Weatherman routine to a long-haired stoned hippy. Carlin said he wasn't aware there were children in the audience and claimed as he was leaving the stage he detoured to dispose of a gram of cocaine. Bullshit. He had been warned not to do the Seven Words. Summerfest was still family oriented and it was fairly early in the evening. Police were waiting for him in the wings; there was no cocaine disposal detour. And Carlin cried in the bullpen and jail cell which also gets omitted. But the national publicity worked wonders for him.