They would probably protect Peter immediately. Maybe they take him to a safe place within the Avengers compound.
The Avengers might start an investigation of their own. They could use their resources to find out who is abusing Peter and gather evidence. They may also provide Peter with emotional support, like having someone like Steve or Natasha talk to him and make him feel safe. They would also ensure that Peter has access to medical care if he has any physical injuries. And they would likely confront the abuser once they have enough evidence.
They might notice signs like Peter being overly withdrawn, flinching at sudden movements, or having unexplained injuries.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.
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.
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.
Some Avengers might be initially shocked. For example, Steve could be a bit taken aback as he tries to understand how this could be possible. He might be concerned about the implications for the team dynamics.
Well, it could be due to misunderstandings. Fanfics often play with the idea that Peter, being young and inexperienced, might accidentally cause trouble that the Avengers misinterpret as intentional. For example, he could be trying to help but ends up making a situation worse, leading to the Avengers' dislike. Another reason could be that some writers like to create drama by pitting characters against each other. They think it makes for a more interesting story if the Avengers have this negative view of Peter Parker, even if it goes against the more positive portrayals in the official comics or movies.
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.
Tony Stark might use his quick wit and technology. He could immediately scan Peter to make sure there's no physical danger causing the hyperventilation. Then he'd probably crack a joke to try and calm Peter down, like 'Kid, you breathe any faster and you'll fly away like a human jetpack.'
They show him kindness and try to understand his motives. They offer support and help him find a better path.
One great 'Avengers take care of Peter' fanfic could be where the Avengers teach Peter different combat skills. For example, Tony Stark might show him advanced tech - based fighting moves. Another could focus on the emotional support they give him. Maybe after a tough mission, Natasha Romanoff helps Peter deal with the trauma. And then there are those where they take care of his daily needs, like Steve Rogers making sure he eats well.