A defensive system in which a player (usually a marking back) will be assigned responsibility to mark a specific individual opponent. Often used to neutralize a particularly dangerous and mobile attacking player; if the strategy is effective, the neutralized player is said to have been "marked out of the game". See zone defense.
Man-to-man defense is a type of defensive tactic used in basketball and Football (Soccer) in which each player is assigned to defend and follow the movements of a single player on offense. Often, a player guards his counterpart (e.g. center guarding center), but a player may be assigned to guard a different position. The strategy is not rigid however, and a player might switch assignment if needed, or leave his own assignment for a moment to double team an offensive player.