Being the Stage Manager’s (SM) right hand person, an Assistant Stage Manager (ASM) is usually called in when the production becomes too large for the SM to handle alone. While the SM is usually in the booth, with a bird’s eye view over the stage, the ASM is just offstage, but not fully backstage, in order to get everywhere at once quickly. This is because an ASM should be able to complete necessary set changes, help with an actor needing to quick change (change from the current outfit to the next in a matter of seconds), or run backstage to drag an actor for their cue.
What the Stage Manager does can also apply to the Assistant Stage Manager. Some of their shared tasks can include taping down where furniture and set pieces will go, be “on book” for the actors (read the first part of the line when they have forgotten it), setting up the rehearsal space before the show (sweep, mop, put furniture and set pieces in place, check props), and ensures that everything is in the correct place before the theatre is locked up for the night. This can often lead the Assistant Stage Manager to spend as many hours as the Stage Manager to keep the production running at peak condition.