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A Broadway example
The Broadway League lists Chicago standing-room tickets at $27 at the Ambassador box office, day-of when the show is sold out, with a limit of two per person. Recheck the policy and availability at the box office before making a special trip.
Questions to ask
Ask exactly where the spot is, whether the floor is level, whether there is a rail and whether any part of the stage is obscured. If you need a seat or cannot stand through the runtime, compare a seated rush option or contact the theatre about accessible seating. Make sure everyone in your group is comfortable with the arrangement.