flash crowd

noun3

1. •
   A large audience for a sporting event that is unexpected because of large numbers of game-day ticket sales rather than advance tickets.

   • Sure, you'll get trapped once in a while with a flash crowd. Like the first time Satchel Paige pitched in Cleveland. We thought we'd get 55,000, and we ended up with 78,000. — 1972
2. •
   A crowd that forms suddenly.

   • The mall riot was the first successful riot in twenty years. “The police can get to a riot before it's a riot,” said McCord. “We call them flash crowds, and we watch for them.” — 1971
3. •
   (no longer used) The fashionable public.

   • To see the Hurst with tents encamp'd on, Look around Lawrence's at Hampton, Join the flash crowd (the horse being led Into the yard, and clean'd and fed); Talk to Dav. Hudson and Cy. Davis. — 1880