When one reads the Prologue to Sharon Pollock's Walsh, it is difficult to understand it; it has much more meaning when the reader returns to the Prologue after finishing the play. However, without being certain of the implications of the players' interactions, it is easy to see that Walsh is the subject of the play, even without referring to (or even knowing) the play's title.
When the Prologue begins, we can draw inferences to who and what is important through the stage direction. Note Walsh's entrance; as he walks to his table...
All the characters watch him.
The lighting also allows for the importance of Walsh's character:
...Walsh appears in a spotlight somewhat brighter than the general dim lighting.
While the lighting is dim throughout the Prologue, and some characters are shown first in the shadows, the audience's attention is drawn to Walsh through the use of the spotlight. When the lights come up slightly, the spotlight disappears, but the deference showed by several of the characters towards Walsh indicates that he is important. For instance, when the Prospector asks Jennie to sing another verse of her song, she defers instead to Walsh:
Is there somethin' else you would have me do, Mr. Walsh?
Harry enters and takes out his "poke," but is warned by Billy and the Prospector to put it away, for Walsh, they indicate, is a force to be reckoned with.
Even the conflicts present in the Prologue include Walsh. When he first enters, the Prospector stops his progress:
The PROSPECTOR is blocking WALSH'S way and WALSH stops. The PROSPECTOR steps aside and WALSH continues toward the table.
And Billy's anger is obviously directed at Walsh, though we cannot understand this before reading (or seeing) the play in its entirety:
To hell with Mr. Walsh.
The violence of the Prologue also comes from Walsh. When "Garryowen," the marching song played when Custer went into battle, is played, and Custer's death is spoken of by Harry, Walsh "bangs down his glass." He then announces to the room who Custer was.
Conversation centers on Walsh who is no longer with "the force," but is the Commissioner of the Yukon. In general, those in the room focus a great deal of attention on Walsh. The hint of conflict between Walsh and the Prospector (when the Prospector blocks Walsh's path to his table) comes to blows when the Prospector (really Sitting Bull) asks Walsh for money for Joeie (who is actually Sitting Bull's son)—because the boy and his mother are starving. The Prospector accuses Walsh's "kind" having "taken enough off us." Twice Walsh responds:
I can give you nothing.
This reflects Walsh's position with Sitting Bull and his people later in the play. However, when the Prospector calls him a "cheap son-of-a-bitch," Walsh hits the Prospector, knocking him down—foreshadowing the physical altercation that takes place between the two men—the two friends—also later in the play.
As all the characters seem prepared for more fighting, Harry addresses the audience and identifies Walsh: his former career with the Mounties and the end of that career. Harry's concentration on the character of Walsh, along with the conversations with and about Walsh as well as the actions of the characters, also lets us know that Walsh is at the center of this story.
Aside from the title--which is an immediate give away that needs little in the way of corroboration--Pollock foregrounds Walsh's centrality be having him be the first to enter in the Prologue and by emphasizing that the dialogue is from Walsh's point of view:
The scene is from WALSH's point of view .... WALSH enters. He is walking very slowly and carefully ....