The Camelot Code, Book 1: The Once and Future Geek - Mari Mancusi

When young Arthur of Camelot accidentally time-travels to the 21st century and Googles himself, he discovers the not-so-happily ever after in store for him once he pulls the sword from the stone. Yes, he'll go from squire to sovereign basically overnight, but he'll also lose the love of his life to his best friend and eventually die in battle. What's a once-and-future king to do? Easy: stay in the future, where he'll actually have a future - and join the football team instead.