Attack Position (攻撃形式, Kōgeki Keishiki, called Attack Mode in the anime) is a Battle position in which a Monster Card is face-up in a Vertical Position. In this position, the ATK value is used to represent this card, except where a card effect requires a specific examination of the DEF value.
Attack Position monsters should always be face-up. The only time when a face-down Attack Position Monster Card is acceptable is when it is placed that way by the effect of "Darkness Approaches"; there are no other cards involving face-down Attack Position. However, most players tend to ignore this rule because they refer to face-down Defense Position Monsters as face-down Monsters.