Can a goalkeeper and a field player change positions at any time during the match?

The correct response highlights that a goalkeeper and a field player can indeed change positions during a match, but this change must occur only during a stoppage of play and requires the referee's permission. This rule is essential for maintaining the structure of the game, as the role of the goalkeeper is specifically regulated due to the unique responsibilities they have, particularly regarding handling the ball within their penalty area.

When a substitution is made, it is standard protocol to notify the referee, ensuring that the game remains organized and that all players are aware of their positions on the field. This rule helps to prevent confusion and maintain the flow of the game while ensuring that the referee has the final say in any positional changes involving key roles like that of a goalkeeper.

Allowed changes at any time, or strictly during halftime, would not consider the requirement for stoppages and referee notification, which are crucial for the game's conduct. Therefore, option B encapsulates the necessary rules regarding position changes between goalkeepers and field players during a match.