Final answer:
In 'Roller Girl', three whistles signal the end of a jam in roller derby, indicating players should stop their current activities.
Step-by-step explanation:
In the book Roller Girl, three whistles indicate the end of a roller derby bout. Roller derby is a contact sport played on roller skates, and it involves two teams competing against each other.
When the referees blow three whistles, it signifies that the match is over and all the players must stop skating.
In the book Roller Girl by Victoria Jamieson, three whistles typically signal the end of a jam in a roller derby match. Jams are the main periods of play in roller derby, where both teams have the chance to score points.
The game is fast-paced and physical, and the referees use whistles to control the flow of the match.
Hence, when the referees blow three whistles, it indicates that the jam has come to a complete stop, and players are expected to cease their current activities.