What instance requires a player to call a judge during a game?

Players should always feel empowered to seek assistance from a judge whenever they are uncertain about a game situation or if they suspect a rule violation has occurred. This ensures the integrity of the game and provides a clear pathway for resolving issues that can arise during play.

The rules and procedures in Magic: The Gathering are complex, and players may not always have the clarity needed to make a fully informed decision on their own, especially in high-stakes tournament environments. By calling a judge, players can receive authoritative guidance that clarifies the rules, resolves disputes, and helps maintain fair play.

In contrast, asking for a card explanation alone is not always a reason to call a judge; it could often be addressed with a simple discussion among players. Additionally, a card effect resolving is part of the normal flow of the game and does not necessitate judge involvement unless there is a specific issue related to how that effect was executed. Lastly, a player's winning position does not inherently require a judge call; it’s more about situations where uncertainty or potential rule infractions arise that warrant a judge's expertise.