This Ability prevents other Pokémon from forcing it to switch out or flee with a move (Roar, Whirlwind, Dragon Tail or Circle Throw) or item (Red Card). Suction Cups does not affect the Pokémon switching out manually, or switching out or fleeing with its own move (Teleport, Baton Pass, etc.) or item (Eject Button).
A Pokémon with the Ability Suction Cups cannot be forced to switch or flee even if it is Ghost-type or holds a Smoke Ball or Shed Shell.
If a Pokémon with Suction Cups is under the effect of Ingrain, Suction Cups will take priority over Ingrain if it would be forced to switch or flee.
Outside of battle
This section is incomplete. Please feel free to edit this section to add missing information and complete it. Reason: In Generation VII, does Suction Cups only make Pokémon fishing encounters more common, or does it make hooking anything more common?
From Pokémon Emerald onwards, if a Pokémon with Suction Cups is in first place in the player's party (even if fainted), bites will occur more often while fishing. Sticky Hold has the same effect.