Wikipedia isn't about "common knowledge" it's about verifiable knowledge. Without a source a statement like "most modern battles are prewritten weeks before the actual battle" is at best "original research" but is actually highly problematic because there is no qualification. Battles happen all over the world and what might be true in one area may not be true in another. Given that this is an article on freestyling defined as an improvised form of rap it should focus on freestyle battles, not prewritten battles as they are not relevant to the page. A reference of this length to prewritten battles certainly has no place in the first paragraph of the page which should be dedicated to a clear and concise definition of freestyling not a discussion of prewritten battles.