It could be that Peter's immaturity showed in a crucial situation. He might have been over - confident and tried something really risky without thinking it through. The Avengers, being more experienced, would be frustrated with his recklessness and thus yell at him. They want him to learn and grow, but his actions might have been too much to tolerate at that moment.
Peter might be very defensive at first. He could argue back, trying to explain his actions. After all, he is a teenager with his own ideas and he may think that the Avengers don't fully understand his perspective.
It could also be due to jealousy. Peter might be getting too much attention from the public or other superheroes. His youth and new - found popularity could make the more established Avengers feel overshadowed, leading to feelings of resentment towards him.
He might also get angry. Peter has a strong sense of justice. If he feels that the Avengers are being unfair, he could stand up to them. He'll use his quick wit and his powers to show that he's not going to be pushed around easily.
One possible reason could be a misunderstanding. Maybe Peter accidentally gets involved in something that looks bad to the Avengers, like being in the wrong place at the wrong time during a security breach. So they misjudge him and are mean as a result.
They might notice signs like Peter being overly withdrawn, flinching at sudden movements, or having unexplained injuries. Maybe they see him constantly on edge around certain people.
In some fanfics, Peter might faint due to overexertion. He's often depicted as being involved in intense battles or using his powers to the extreme. For example, if he's been fighting a powerful villain for a long time without a break, his body could just give out and he faints.
Another reason could be related to Peter's mistakes. He may make errors during a mission that put the whole team or the city at risk. Tony, who has a lot of responsibility on his shoulders, might yell at Peter as a way to make him understand the seriousness of his actions and to prevent future mistakes.
Obviously, Peter Parker is one of the main characters. And then, the Avengers members like Tony Stark, Steve Rogers, Natasha Romanoff, etc. are also main characters as they are the ones adopting Peter. They play important roles in Peter's new life and in the overall story.
Most official and well - received fan works are based on the positive aspects of the characters. Peter Parker is a character with great potential for stories about growth, mentorship in the Avengers, and his own journey as a hero. So, fanfics with inappropriate content are not in line with the general spirit of the franchise.