Stealth Rock sets an entry hazard around the target Pokémon. Pokémon on the target's field receive damage upon switching in. The amount of damage inflicted upon switching in is affected by the effectiveness of Rock against the target. It also does not stack if multiple layers are set. It does not damage Pokémon with the Ability Magic Guard. Rapid Spin removes Steath Rock from the user's side of the field if it affects its target; Defog clears the Stealth Rock from both sides.
The damage is taken from the victim's maximum HP, and follows:
Damage (Max. HP)
The user lays a trap of levitating stones around the opposing team. The trap hurts opposing Pokémon that switch into battle.