You will need to have the service already through a TV provider. Just like the 360 works now to watch certain TV providers like Fios. Only hopefully with the xbox one it works better to the point where it isn’t easier to just use the cablebox from the cable company.
As far as the NFL deal goes, I think DirectTV still has the exclusive on it, so not sure how they would allow for full game packages. I am thinking maybe they will just be doing overlays of stat data and things like that while you are watching a game through your provider.