Hey all, as the title says I'm looking for advice on shooting ultimate frisbee. I've played the game for a few years now (still do) and just recently I've begun photographing some of my teams tournaments and games. I've had some luck but have been extremely limited by my setup. I only have a Canon XSi, the kit lens, and a nifty fifty. Not the best setup for shooting fast moving action that can be at some distance away from where you're standing since the game moves relatively quickly so I was wondering if you guys could help me out with lenses.
For those who don't know (probably most of you) an ultimate frisbee field is 37m wide, and 100m long (including the two 23m endzones on either side). With my current setup I've only been able to stand super close to the action and before I know it the disc is all the way down field. So my question is thus: What focal length do you think would be best suited for this sport? If you have a specific lens recommendation I'd like to hear that as well.
I've been looking at a Canon 70-200mm f/4 nonIS because it seems like a good reliable lens for the money and its pretty much the extent of my budget but I'm not sure if its the best focal length. What do you guys think?

