Starting from Generation V, Speed Boost will not activate at the end of the turn if the user failed to escape from a wild encounter during that turn. It will activate if the Pokémon is switched in due to a previous Pokémon fainting. Speed Boost will not activate on the turn the Pokémon with the Ability is switched in (even if it gains the Ability after switching in). At the end of each turn, Speed Boost raises the Speed stat of the Pokémon with this Ability by one stage.
