Narrowing the Field: Sudden Death Elimination!

is episode 38 of the original Naruto anime.

Synopsis
Hayate announces that an unusually large number of genin passed the second stage of the exam, and as such, before they can proceed to the final stage, a series of one-on-one preliminary matches will have to take place so that only the winners of each match can proceed. Kabuto drops out immediately upon the notice, attributing his withdrawal on an injury sustained from an earlier part of the test; however, he worries to himself that if he participated, the "old Kabuto might come out". Sasuke is still experiencing pain from the cursed seal, so Sakura tries to convince Sasuke to drop out. Sasuke refuses, and says that although he doesn't actually care about becoming a chūnin, he must see how he does against some of the best new ninjas so he can avenge his family. The preliminary matches are to begin with Sasuke versus Yoroi Akadō. As everyone else leaves the arena, Kakashi walks up to Sasuke and warns him about using his Sharingan, revealing that he knows about the cursed seal. He tells Sasuke that if the cursed seal begins to overtake Sasuke, Kakashi will stop the match.

Trivia

 * Orochimaru in disguise is shown wearing a Konoha forehead protector instead of an Oto one at a point.

es:Reduciendo campos: ¡Eliminación por muerte súbita!