Lots of interesting advice here about low light shooting, but for me, super fast lenses are not an option. I am not a rich person or a pro, I can only afford relatively slow longer lenses myself.
As my kid graduated yesterday and I was in exactly the same situation myself as TCOLE1983 was, here are a few tips I got from a sports pro photographer several years ago and I hope these might help someone else as they saved the day for me:
1. Get to the venue early. This lets you scope out the best location to shoot from and get practice shots in without being rushed. You can then know what works and what does NOT work. This lets you PLAN for the best shots and know what not to bother with; less stress and a better chance of success. Also sit on the end of the row of seats (see #4).
2. Use a monopod. When you are in a poorly lit stadium (as I was), a monopod is useful when a tripod is not permitted or possible.
3. Stand up. It might be rude to those behind you, but if you are there early (see #1) you can practice this to get good and quick at it. Lets be honest, being "up" for a few seconds when you HAVE to so you get the one shot you need, is better than missing it! Many photographers will tell you to overcome the embarrassment of getting in the way of someone who is waiting for their kid/wife/whatever to walk across the stage, which 99.999% of the time won't be for ages yet.
4. Stand on the stairs. I did a few shots adopting the "tripod position" (with the monopod as one leg of the three of course) standing on the otherwise almost empty stairs next to the row of seats I was in (seated on the end seat makes this EASY).
5. Use a monopod. I said that already, but reason #2 for this is that the best I know I can do hand held at the venue without flash (I was about 60 yards from the stage and using a 70-200mm lens) was right on the border of visible shake. Using a monopod lets me be almost 100% steady, so I was able to also use MANUAL settings... No flash at 1600ISO, 1/60th to 1/125th at F5.6-ish and I got a series of slightly noisy but well lit and tack sharp shots with just a small touch of movement blur showing where people were walking or waving fast. In short, while not perfect, I got the shots.
If I had something like a D7000 I might have been able to go to 3200ISO and a higher shutter speed and get lower noise levels, but I don't (yet), so that's just too bad. You can't worry about the things you can't control and I did at least get the shots I wanted.