What do you do if your book straddles several genres? Do you just market it to people using the genre that seems most prominent and immediate?

For instance, my book could easily fall into both a spy thriller genre and a sports genre, and both would be immediately and equally the first thing that could come to mind. Of course, there are other elements of other genres present, but I'm sure that's the case with many books out there.

So do I just go with one genre or both? It might make it difficult for bookstores or other potential readers to know what it's like because they might be into one and not the other.

Any ideas?