My understanding of copyright as it relates to fanfiction is that as long as an amatuer author is not profiting from their fanfiction, they are not infringing on the original author’s copyright. Since the author’s work is considered intellectual property, any profit would be considered copyright infringement. There is also a debate as to whether fanfiction falls under fair use, where an intellectual property can be used for the purposes of criticism, parody, or education. However, despite fanfiction being legal if it is not making money, many authors discourage it or outright ban it.