"The Training Commences" (修業開始, Shūgyō Kaishi) is chapter 18 of the original Naruto manga.
To improve their chakra control, and thus the effectiveness of their techniques, Kakashi teaches Team 7 how to climb trees. Naruto fails completely, Sasuke can only make it halfway up, and Sakura is able to make it to the top on her first try. After repeated failures, Naruto asks Sakura for tips. Meanwhile, Zabuza recovers from his fight with Kakashi. Gatō approaches him intending to kill him for his failure, but is stopped by Haku, who breaks Gatō's arm in punishment for even considering touching Zabuza. Zabuza assures Gatō that he will finish the job in a week's time.