This Ability prevents other Pokémon from forcing the Pokémon with this Ability to switch out or flee with a move (e.g. Roar, Circle Throw, etc.) or item (Red Card). Suction Cups does not affect the Pokémon switching out manually, or switching out or fleeing with its own move (e.g. Baton Pass, Teleport, etc.) or item (Eject Button).
Even if the Pokémon with this Ability is Ghost-type or holds a Smoke Ball or Shed Shell, it cannot be forced to switch or flee. If a Pokémon with this Ability 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.
In Pokémon Super Mystery Dungeon, Pokémon with this Ability cannot be blown away (such as by Roar or Whirlwind Wand), or warped, but can be forced to move (such as by Baton Pass or U-turn).