Which infraction occurs when a player looks at the faces of an opponent's cards while shuffling their deck?

The correct answer is that this situation is classified as a Manipulation of Game Materials infraction. When a player looks at the faces of an opponent's cards while shuffling their deck, it can compromise the integrity of the game by gaining an unfair advantage. This behavior falls under manipulation because the player is interacting with their opponent's game materials in an improper way, which can lead to an uneven playing field. Respecting the boundaries of card visibility is crucial in maintaining fair play and ensuring that each player adheres to the rules of the game.

The focus here is on how handling game materials—specifically, cards belonging to an opponent—can disrupt the integrity of the game. This type of action suggests an intention to gain knowledge about something that should remain hidden, which is not only against the rules but also undermines the trust required for a fair match. It's important for players to only interact with their own cards and game materials under the established guidelines.