No way around it. If you're going to shoot sports, you NEED f/2.8 and you NEED long lenses. For football I take nothing less than two cameras, the 70-200 f/2.8L II IS, and the 400 f/2.8L I IS. With a 1D4 I was using the 300 f/2.8L I IS more and I still will if I get super close along the sidelines. Either way, I'm always shooting at f/2.8 as well.
With a 7D? Factoring in the reach, the 70-200 f/2.8L II IS lens would probably cover everything for you, except the short end in this case. But, who cares? Just back up. It's a good decision for you and one that you will NOT regret.