Hey, someone asked a similar question recently, here's what I told them:
If you're interested in sports medicine and orthopedics, you might consider checking out the University of North Carolina, Chapel Hill, they offer a paid residency program in orthopedics for FNPs:
I don't think it's strictly necessary, but it would undoubtedly help
If you want to be an NP with a focus on sports medicine I get the impression that it's possible, however, I have no idea how many opportunities there are for it. Let me know if you do learn more though, I was once kind of torn between the nursing route and physical therapy, and I'm still interested in sports medicine.