The Pokémon's Defense stat cannot be lowered by other Pokémon's moves or Abilities.
Big Pecks (Japanese: はとむねPigeon Breast) is an Ability introduced in Generation V.
Effect
In battle
Big Pecks prevents other Pokémon from lowering the Defense stat stage of the Pokémon with this Ability. It does not prevent the Pokémon with this Ability from lowering its own Defense, such as by using Shell Smash. It does not prevent Spectral Thief from stealing (i.e., resetting) positive stat changes.
Effects that decrease Defense without using stat stages, such as Guard Swap, Heart Swap, or Guard Split, are unaffected by Big Pecks.