When swordfighting became a trouble (Sword fighting competition) (剣道はメンドウでござるの巻) is episode 615 of the Ninja Hattori-kun 1981 anime.Hattori teaches Kenichi how to duel.
Kemumaki is boasting to Kenichi and Yumeko about his skill of duelling. As Yumeko praises Kemumaki, he nastily insults Kenichi, saying that he wouldn't know a thing about sword-fighting. Kenichi nearly punches him in his anger.
Back at home, Kenichi begs Hattori to teach him how to duel. Hattori is disdainful, but grudgingly agrees for Kenichi's sake. Kenichi then sets about impressing Yumeko. Later on in the garden, Kenichi duels Shinzo and Shishimaru, but ends up getting injured.
As Shinzo nurses Kenichi's injuries, Kenichi comes up with an idea: to eat have a nice cream tea. As Hattori, Shinzo and Shishimaru all collapse, Hattori comes up with an idea himself: to teach Kenichi to strike when the opponent is distracted. Kenichi is more determined than ever.
Next day in the school boxing court, Kenichi prepares for the duel when Kemumaki turns up, flanked by Yumeko. Kemumaki taunts Kenichi saying that Hattori will undoubtedly substitute him - and Yumeko outrageously sides with him. Kemumaki then ties Hattori up and orders Kagechiyo into sight. In he comes, dragging a frog along with him. Hattori nearly jumps out of his skin with fright.
Later on, Yumeko starts the duel. As Hattori squirms in perpetual fear of the reptile, Kenichi and Kemumaki start the duel. Kemumaki bashes Kenichi with his sword, just as God puts an idea in Hattori's mind. He agitates Kenichi so much with his screams of fear that his trousers slip. As Kemumaki stops dead in fright, Kenichi sees his chance and defeats him with a bash of his sword. As Yumeko, Shinzo and Shishimaru congratulate him, Hattori struggles desperately to get away from the frog.