In theatre, we have what we call: a swing, an understudy and a standby. Three distinct, respected functions. There can a handful of these actors in the same shows for the lead roles, depending on the budget and the roles’ physical demand. Knowing that Broadway shows run eight times a week, it is very important that someone will be able to rock that stage no matter what.
In major Broadway productions, you can usually find performers hired to learn the track (the choreography and lines of a particular role) and ready to jump in at any point during the show if needed.
A swing wears at least two hats. They can “swing” between two parts in the same show. Lots of ensemble members right now on Broadway are swings to one of the lead roles and perform an ensemble track on a regular basis. Some are ensemble members and can be noted as swing to one of the major lead parts.
An understudy learns the track for when the primary performer is absent. Usually, if the said name is famous, another big name can be called as an understudy for that specific replacement. They are then aware in advance when they will perform.
A standby, literally, is always ready to go on at any time. For example, in the first act, you may applaud one lead but applaud a different performer for the same role in the second act. If a standby isn’t there for such an occasion, the production can ask a swing. A standby has to be backstage at all time, warmed up, made up, and costume-ready so that the show can move on smoothly if the original actor cannot perform their role.
It is important to know that after the previews, all shows are “frozen,” which means that the blocking and choreography are locked. Therefore, each performer who learn each track must be very thorough and respect the writer, director and creator’s visions, not deviating from what has been locked.
Each of these jobs are crucial to the theatre industry — just as crucial as the primary leads and no swing, understudy, or standby is less talented whatsoever. Many will go through months of long auditions and are cast on the same criteria as the leads.
The beauty of a company is that initially, everyone knows the track of one another. There are of course official swings, understudies, and standbys though. The quality on stage is delivered to its best no matter who performs.