Why was Kakashi Hatake doing all of the hard work in the episode when they first fought Zabuza? Naruto, Sakura, and Sasuke were standing back, and Kakashi was fighing Zabuza all by himself. Why?
At that time, the members of Team 7 has just passed from the Academy, they were just kids. Sakura couldn't help much because she was very weak, she hadn't learnt medical ninjustsu to reinforce her punches. Sasuke may have been a bright child but he was still an amateur and he hadn't awakened his Sharingan. Even if he had awakened it, Zabuza was a formidable opponent, one of the Seven Ninja Swordsmen. And Naruto didn't know any jutsu other than Shadow Clones, and he didn't have control over Kurama's power. But Naruto and Sasuke did fight against Haku if not Zabuza. It's obvious that the strongest team member Kakashi should fight against Zabuza since he's so strong.

P.S. I think you have not watched the Naruto series and you've only watched the Shippuden series.