Pokémon Season 1 Episode 4

Challenge of the Samurai
While wandering through Viridian Forest, a Samurai challenges Ash to a battle, and it turns out to be Metapod vs. Metapod. After a short time, a swarm of Beedrill attacks, and Ash’s Metapod is taken by them. Ash is able to rescue his Metapod and it evolves once more into Butterfree.