noun

• (figurative) An incidental spectacle that diverts attention from a larger concern.
  "Far from learning from the failures of ‘economic rationalism,’ the Liberals want us to swallow more of the snake oil medicine while diverting our attention to the consumption tax sideshow."
• (US slang) An incident in which drivers block traffic to perform stunts like donuts and burnouts for an extended period of time.
  "The spontaneous street party is the center of Oakland's recently developing Hyphy culture, but has a long history in Oakland car culture and hip hop. A sideshow is essentially a spontaneous street party in which one might “ghostride the whip” (get out while driving), “gas brake dip,” or even “scrape” (spin donuts in the middle of the street)."