Yes, there might be such fanfiction out there in the vast world of fan - created content. However, this kind of plot is quite dark and not in line with the typical heroic and collaborative image of the Avengers and Spider - Man in the mainstream comics and movies.
It could be due to a mind - control device. Some evil force might be controlling the Avengers and forcing them to torture Spider - Man. This would add an element of helplessness to the story as the Avengers are not acting of their own free will. Another reason might be a deep - seated jealousy within the Avengers. Perhaps they feel that Spider - Man is getting too much attention and they want to put him in his place, which is a very dark and out - of - character take but possible in the realm of fanfiction.
No. Fanfiction about Spider - Man usually focuses on his powers, his battles against villains, and his relationships. Torture is a rather dark and disturbing theme that doesn't fit the general tone of most Spider - Man fanfictions.
Well, maybe he's got some secret mission that he doesn't want the Avengers to interfere with. You know, like protecting a particular person or some crucial information that he thinks the Avengers might mess up if they get involved.
Another possibility is that the Avengers are being manipulated by a villain. The bad guy could be using false information to make the Avengers believe that Spider - Man is a danger. So they go after him without really knowing the truth.
Spider - Man would likely be confused at first. He respects the Avengers and can't understand why they are suddenly after him. He might try to talk to them, to explain that he's innocent. For example, he could swing up to Captain America and start pleading his case.
Spider - Man would probably be shocked at first. He looks up to the Avengers and being kidnapped by them would be the last thing he expects. He'd likely try to talk his way out, using his quick wit and charm. He might start by asking why they're doing this and try to convince them that they've made a mistake.
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.
Spider - Man would probably be defensive at first. He's used to working alone most of the time, and being interrogated by the Avengers would seem unfair to him. He might crack some jokes to ease the tension, but also firmly state that he's a hero too.
It's highly unlikely that the Avengers, as fictional characters in their own right within the Marvel universe, would actually sit down and read Spider - Man fanfiction. They are usually too busy saving the world or dealing with their own personal dramas. Fanfiction is more of a concept for the fans in the real world.