Arena Trap is a Pokémon ability introduced in the third generation. It prevents grounded foes from fleeing.
When a Pokémon with Arena Trap enters the field, grounded opponents cannot flee or switch out until the Pokémon remains in the battle. Flying types and Pokémon with Levitate are immune to Arena Trap as well as Ghost types as of Generation VI. The moves, Baton Pass, U-turn, Volt Switch and Parting Shot, as well as the Shed Shell can also ignore Arena Trap to switch but not to flee. Having the ability Run Away or Smoke Ball can let them flee but not switch.
Outside of battle, if a Pokémon with Arena Trap is in the first place in the party, the wild Pokémon encounter rate increases by 100%. It shares this trait with Illuminate and Swarm.
Pokémon with Ability