For example, in the XY Pokémon league when he was battling Shouta (I think that's his English name). Ash used Talonflame against a Water Type, leaving him at a type disadvantage, resulting in Talonflame fainting. Why didn't Ash switch to Pikachu when the Water Type Pokémon was sent out?
Why doesn't Ash switch Pokémon when a Pokémon with a Type advantage against his current Pokémon comes out?