I shoot a lot of Western sporting events and for the past five years have been using a pair of Canon 7D cameras... much of the time with a 70-200mm lens on one of them and a 300mm lens on the other (and other lenses in my camera bag and car). I'm currently upgrading to Canon 7D Mark II cameras.
Gymkhana barrels, 300mm lens...
Hunter-Jumper, 70-200mm lens (140mm)...
Trail Trials, 28-135mm lens (47mm)...
For fast action shooting, you need camera and lens combo with quick, high performance auto focus. The AF both has to lock on almost instantly
and be very good tracking movement.
Canon 7D-series cameras have a lot of customization tweaks, to set up the AF for best performance shooting various types of action. To do this, they inherited a lot of features and technology from the top-of-the-line, pro-oriented Canon 1D-series cameras. The 70D, T6i and T6s all use an AF system that's similar to the original 7D's, slightly simpler but still pretty much up to the task.
About the most accurate and consistent way to shoot action with any of these is using Single Point (manually selected and usually the center AF point), AI Servo focus mode with Back Button Focusing. There are also some techniques using multiple AF points (Zone Focus, Expansion Points, etc.) 7D-series have the most of those options (aside from the very expensive 1D series).... 70D, T6i and T6s have somewhat fewer... but more than a lot of other general-consumer and entry-level models. The older Canon 60D, 50D, 40D and T5i, T4i are pretty good too, but even simpler so will tend to be a bit more restricted to using the center AF point only for most action.
You then need to complement the camera's capabilities with fast focusing lenses... Canon's USM are, for the large part, pretty hard to beat. Many of them are quite fast focusing... Canon 70-200 zooms and 300mm lenses included. Also, the various 70-300s with USM and both the Canon 100-400s. For closer shooting or somewhat wider shots, 24-70, 24-105 and 28-135 can serve pretty well. Some of the "crop only" Canon EF-S lenses such as the 17-55/2.8 and 15-85mm also have high high performance USM focus (but a lot of EF-S lenses don't). All of the Canon cameras will do better with f2.8 or faster lenses, but that's not always practical (and a lot of the lenses mentioned aren't f2.8... Those tend to be bigger, heavier and often a whole lot more expensive).
IS or image stabilization isn't mandatory when shooting action, because a higher shutter speed is often needed anyway, in order to freeze the action. However, on telephotos like all these IS can be handy for a lot of other things, lets you use slower shutter speeds handheld for other purposes, and it also serves to stabilize the image in the viewfinder, which can be very helpful when trying to follow fast moving subjects.
Canon and Nikon both use lens-based stabilization that will helps with what's seen in the viewfinder (other systems with in-camera, sensor-based stabilization typically don't help this way). I should mention that many Nikon shooters feel, and there is at least some evidence to show that their VR stabilization slows down auto focus slightly. Having used various stabilized Canon lenses for about 15 years, I feel the opposite is true with their IS... that it helps AF perform better. I don't have any real evidence, but it just makes sense to me that a stabilized image would be easier and faster to lock onto and track movement.
All the gear I use is fairly large and not particularly lightweight... doesn't meet your requirements in those respects. I also don't worry about or hesitate to change lenses, either. After all, being able to interchange lenses for different situations is one of the key points of an SLR camera system!
I shoot with Canon and know that system best... That's why I've mentioned it in detail above. This is not to say it's the only choice, though. In fact, I'm sure there are similarly good choices in the Nikon system, in particular. Pentax, Sony and Olympus also have some interesting offerings, although their systems aren't as extensive and comprehensive as Canon and Nikon's. I've worked with other photographers and taught students who have successfully used all these systems.
Oh, and "shooting from a couple football fields away" is going to require a massive lens! I'd suggest you "zoom with your feet" and get a bit closer... or look for something that can be mounted in the back of a pickup truck! :roll:
For example, this was shot whole lot closer with a rather big 500mm lens with a 1.4X teleconverter, on a heavy duty tripod. All together about 20 lbs of gear...
I shoot a lot of Western sporting events and for t... (