So well attended, or (of public transportation) so full, that all of the seats in the venue are occupied, leaving only the ground or the floor for other people. (of an event)
2023 October 12, Neil Johnston, “FA Cup: Why Stourbridge is fearing for its future”, in BBC Sport[1]:
Ever since Stourbridge-born Bellingham became huge news, fans turn out to cheer the local hero on the big screen inside the clubhouse whenever the Three Lions - who play a friendly with Australia on Friday followed by a Euro 2024 qualifier against Italy next Tuesday - are in action. "It was standing room only in here when he played for England at last year's World Cup," Andy Pountney, chairman of Stourbridge, tells BBC Sport.
2024 April 17, “Rural railways: do they deliver?”, in RAIL, number 1007, page 57:
Here [at Grantham], the train has three minutes to reverse, during which time it is suddenly packed out with shoppers heading to Nottingham. It's standing room only for those who arrive last.
