The Enemy: Ninja Dropouts

is episode 209 of the original Naruto anime.

Synopsis
Naruto, Sakura and Lee are hired to escort a "Ninja Dropout" — a criminal ninja — named Gantetsu to prison, and guard him against his comrades, who may be trying to free him. They learn that Todoroki, the captain of the guard, has a personal vendetta against Gantetsu for what happened to his parents and younger brother. During an attack by one of the Ninja Dropouts, Naruto, Todoroki and Gantetsu are separated from Sakura, Lee and the guards.