|Japanese (base text)||
Defense Position (Japanese:
In Defense Position, a Monster Card is always placed horizontally in its Monster Card Zone, rotated 90 degrees counterclockwise from its Attack Position as seen by its owner. When a monster is Set, it is played in face-down Defense Position.
Monsters cannot be Normal Summoned in face-up Defense Position, except by a card effect that allows them to be Summoned that way (such as "Light of Intervention"). During a battle involving a Defense Position monster, the DEF value of that monster is used to calculate Battle Damage, rather than the ATK value.
As Link Monsters do not have DEF, they cannot be Summoned in and/or changed to Defense Position.
Usually, Defense Position monsters cannot attack, but some monsters such as "Elemental HERO Rampart Blaster" and "Total Defense Shogun" have effects that allow them to attack while in Defense Position. In that case, they will still use their ATK for Damage Calculation. Some "Superheavy Samurai" monsters can attack in Defense Position, but apply their DEF instead of their ATK as their ATK during damage calculation.
If Defense Position monster is attacked, the attacked player will take no damage. However, there are cards that inflict piercing damage, which lets a monster inflict damage in this way. If the attacker has lower ATK than the DEF of the attack target, the attacker takes Battle Damage, but neither monster is destroyed. If the attacker's ATK is equal to the target's DEF, neither player takes Battle Damage and neither monster is destroyed.
In the anime
In the earlier anime, a player is able to, and usually does, Normal Summon their monsters in face-up Defense Position without the aid of card effects; if a monster were to be Set, it typically had a Flip Effect. Starting from Yu-Gi-Oh! ZEXAL, this is no longer true, the rules aligned with the TCG/OCG and as such, a player must either Normal Summon a monster in face-up Attack Position or Set it in face-down Defense Position.
Also, the materialized Monster Cards in face-up Defense Position have their said position illustrated; in Yu-Gi-Oh! and Yu-Gi-Oh! GX the monsters will crouch into a defensive pose above an enlarged likeness of the actual card placed in the conventional Defense Position. In Yu-Gi-Oh! 5D's, they become blue-colored. In Yu-Gi-Oh! ZEXAL, the monsters return to simple defensive poses. In Yu-Gi-Oh! ARC-V, they glow with a blue aura. In Yu-Gi-Oh! VRAINS, the monster's appearance remains unchanged regardless of battle position.