It seems as though the key words are "right" -- but the well-known term is most definitely sports book. I have never heard anyone mention "book sports."
If the domain were to be well developed and promoted those key words will certainly help it get into the SERPs. And if you get an early start, might even do better than the "correct" term. So, if developed, it could be a winner--but probably doesn't have too much value at resale for the domain only.
Close isn't always good enough. Sportsbook is both a common term and a prominent brand. Inverting the names may capture some search traffic if a site was well designed but the term booksports has zero OVT and booksports.com won't come up for me. Sportsbook.mobi may have some coattails but booksports.mobi isn't riding them IMO.
Got to agree with the others. It kinda sounds like an term for an agent that would 'book' sport games, like book a band, but I'm not sure that is done for sporting games.