Maybe this clarifies a little:
Ash's opponent in the first battle round is Nando, the Pokémon minstrel. He is a talent who also entered the Grand Festival and had a fierce battle against Zoey. Nando, specialized in Bug and Grass types, sends out Roserade as his first Pokémon. Ash sends out Staraptor who has a type advantage.
But it is Nando and Roserade who take the initiative first. With their unique rhythm and strategy, they attack in angry waves Staraptor is unable to grasp. Ash, knowing that losing his first Pokémon in this short battle would create a huge disadvantage for him, becomes hasty. And then, the match makes an unexpected development.