Haruka! The First Pokémon Contest Challenge!! - S6-E35
Continuity mistake: When Ash suggests that May could check the date for the contest earlier, the buildings on the side change between shots. Also, the left side of his hat constantly changes from red to black. (00:00:03)
Answer: There are a lot of fan theories around this, but the most common theme is that Pikachu had another trainer before Prof. Oak, who gave him to Ash. Pikachu didn't appreciate being handed over.
Ssiscool ★