What happens when Kakashi's bell test goes off script. When Sakura tries to quit as a ninja, thinking the entire test is simply rigged to get rid of her, Kakashi orders Naruto and Sasuke to kill her as a missing-nin. Not only do they refuse to even consider it, but Naruto tells Sakura to run while he and Sasuke fight Kakashi to protect her, refusing to submit even when he threatens to kill them as well for siding with her.
After being generally useless and weak for almost the entire story up to that point, Sakura's first chance to shine comes when Hidan is about to kill Naruto. Despite already being wounded, she unleashes a brief burst of Kyuubi-fuelled rage that empowers her to grab Hidan's scythe so firmly that he nearly loses it, giving Kakashi the opportunity he needs to take him down.
When that doesn't work (since Hidan can even survive a cut throat) things get worse. The Kumo jounin, Tetsu, is taken out, Kakashi is drained enough that he only has one shot left and the remaining genin (and the chuunin Eimi) are petrified by Hidan's massive killing intent. When all seems lost, it's Sakura who makes the difference. First she fights off his killing intent with sheer Heroic Resolve, refusing to allow Hidan to hurt her friends no matter what, then attacks him even though she already has one arm in a sling, slamming into him and biting his hand when he picks her up by her good arm. Finally she makes Hidan stop laughing when she pins an explosive tag to his chest with her injured arm. Even that isn't enough, despite the others leaping into restrain Hidan, and once again Sakura tips the balance, rising from near-unconsciousness to grab his leg and make him stumble, allowing Naruto to catch him with the Chakra Chain Snare and hold him long enough for Kakashi to kill with a Chidori through the heart.
The Kumo team turn on them by trying to take Sakura hostage to make Naruto and Sasuke surrender. Unfortunately for them, they hurt the two boys while subduing them and when they stun Sakura again she's pulled into the seal to meet the Kyuubi. When she comes out again, she unleashes Unstoppable Rage on the team, resulting in a Curb-Stomp Battle. Not even Tetsu is any match for her.