What infraction is defined when a player draws extra cards when his opponent is not looking?

The infraction that occurs when a player draws extra cards while their opponent is not looking falls under the category of Manipulation of Game Materials. This is focused on actions that alter the game state improperly through physical means, such as handling cards in a way that is not allowed by the rules.

In this instance, drawing extra cards constitutes a manipulation of the game materials because it directly affects the integrity of the game setup and the state of play, which should be transparent to both players. One of the core principles of Magic: The Gathering is that all players should have equal access to their game information at all times, and drawing cards without the opponent's awareness violates this principle.

The other choices do not fit this specific scenario. Cheating – Hidden Information Violation pertains to actions that involve concealing information or attempting to gain an unfair advantage related to hidden cards or information. Unsportsmanlike Conduct involves behavior that violates the spirit of the game but does not specifically describe a violation tied to physical manipulation of game materials. Illegal Deck Construction deals with discrepancies in the deck that are not related to card drawing or manipulation during play. Therefore, the correct categorization for this infraction is Manipulation of Game Materials.