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.
Their dynamics would change a great deal. There would be a lot more tension. Some members might blame themselves or others. For example, Iron Man could be at odds with Captain America if they had different ideas on how to handle the situation. Their usual teamwork might break down as they are all dealing with grief in different ways.
Some fans would be very shocked. They are used to seeing Spider - Man as a friendly neighborhood hero and an ally of the Avengers. If he were to hurt them, it would be like a betrayal of the image they have of him. They might feel angry at the character for a while until the story unfolds more and explains his actions.
In the fanfiction, the Avengers would likely be devastated. Captain America might feel a sense of guilt for not protecting Spider - Man better. Iron Man could be filled with rage and vow to take revenge on whoever was responsible. Thor would probably be solemn and use his strength to seek justice. Overall, their reactions would be a mix of grief, anger, and determination.
They would probably have a range of reactions. Some might be entertained, while others would be more critical. Stark might joke about the science in it not being as good as his own tech.
The Avengers would be very concerned. Captain America would immediately take charge of the situation, trying to keep everyone calm while they assess Spider - Man's injuries. Iron Man would start scanning for the best way to treat him, using his high - tech equipment. Thor might offer some of his Asgardian knowledge of healing, if there was any. Black Widow and Hawkeye would be on guard, making sure there were no further threats while the team focused on Spider - Man.
Spider - Man fanfiction often showcases the creativity of the fans. For instance, there are fanfictions that put Spider - Man in crossovers with other superheroes or even in different historical settings. I think it's a great way for fans to express their love for the character and expand on the Spider - Man universe that we know from the comics and movies.