Answer: understudies

AnswerCrossword Clue
UNDERSTUDIESWaiters in the wings
UNDERSTUDIESBroadway backups
understudies(in the theater) A person who learns another's role in order to be able to act as a replacement at short notice
understudiesUNDERSTUDY, to act another's part or take over another's duties