There are fanfics where the Avengers capture Spider - Man because of a false accusation made by a jealous superhero. This leads to a whole adventure where Spider - Man has to prove his innocence. Also, sometimes in these stories, it's part of a bigger plot to test Spider - Man's loyalty or to train him in a very unorthodox way.
One possible fanfic could be where the Avengers capture Spider - Man because they misunderstand his actions. Maybe they think he's working for an enemy when he's actually on a secret mission to help them. Another could be a story where a villain tricks the Avengers into believing Spider - Man has gone rogue.
Well, in some fanfics, the Avengers might capture Spider - Man due to a miscommunication about his new powers. They could be worried that he's become a threat without realizing he's still on their side. There could also be a fanfic where the Avengers are under mind control and they target Spider - Man for no good reason.
The Avengers might capture Spider - Man if they suspect him of being involved with a new, unknown threat. For example, if there are strange crimes happening in the city and Spider - Man is seen at the scene every time, they could assume he's part of it.
One reason could be a misunderstanding. Maybe some events were misinterpreted, and the Avengers thought Spider - Man was involved in something bad. For example, if there were some crimes that seemed to have Spider - Man's fingerprints all over them, but in reality, he was being framed.
One interesting storyline could be Spider - Man teaming up with the Avengers to fight a new super - villain that's a combination of different powers they've faced before. For example, a villain with the strength of the Hulk and the mind - control abilities of Loki.
One interesting Spider - Man Avengers fanfic could be 'Spider - Man's New Allies in the Avengers'. It might show how Spider - Man adjusts to being part of the big superhero team. Another could be 'Spider - Man Saves the Day for the Avengers' where he uses his unique skills to get the Avengers out of a tough situation. There are also fanfics that focus on his relationships with individual Avengers, like his mentorship under Iron Man.
Spider - Man would be very confused. He would feel betrayed because he thought the Avengers were heroes he could trust. He could start by asking them why they are doing this. If they don't give him a satisfactory answer, he might try to escape in a sneaky way, using his spider - like abilities to find a weakness in their capture setup while still trying to reason with them.
One reason could be that they suspect him of being involved with a new villain's scheme without having all the facts. So they act preemptively and capture him.
One possibility could be that the Avengers capture Spider - Man because they suspect he has been influenced by some sort of mind - control or dark magic. Maybe they think he's a threat to the city without realizing he's actually trying to help. Another could be that there's a misunderstanding in which Spider - Man's actions are misinterpreted as being against the Avengers' interests.
Spider - Man could use his agility and web - slinging skills to escape. He could swing between buildings, making it difficult for the Avengers to follow him. His small size compared to some of the Avengers also gives him an advantage in hiding in tight spaces.
One possible reason could be a misunderstanding. Maybe the Avengers think Spider - Man has been compromised by some sort of enemy influence. For example, if a powerful villain has the ability to control minds and they suspect Spider - Man is under that control, they would try to capture him to protect the world and also to try and break the control. Another reason might be that they believe Spider - Man has some information that is crucial for saving the world but he's being uncooperative, so they resort to capturing him. It could also be that there's some sort of new law or regulation in the superhero world that Spider - Man is unknowingly breaking, and the Avengers, as the enforcers of a sort of superhero code, feel they need to bring him in.
Spider - Man would probably be very confused at first. He looks up to the Avengers and would wonder why they are after him. He might try to talk to them and explain that there has been a mistake.