I also take a Nikon 7000 with a Sigma 120-400 to field sport. The Sigma is a great lens and adds some punch to my kit. However, the Nikkor 80 - 200 with its constant F2.8 is probably the most versatile piece of equipment that I own. It is excellent for sport, portraiture, and nature.
The 80-200mm lens is one of my favourite lenses for both sport and nature photography. This shot was taken in a match Campbelltown and Barker Old Boys in western Sydney. It was one of many matches played in a very large amateur rugby competition.