It's a HS game, so is it safe to assume you will be able to move around the gym and get relatively close to the action?
If so, you'll probably do best with the large aperture on the 50mm. Lens speed is a priority when shooting indoor sports.
If you're stuck in one place up in the stands, and can't get closer to the action you'll want the zoom power of the 70-300 but will be fighting the combination of low-light and high-speed action.
I would take both, try to shoot as much from the sidelines with the 50mm as I could, and use the 70-300 to try some pan shots from the stands, and slower moving things like candids of the coaching staff and bench, fans, etc.
(Message edited by Mammoth on January 06, 2009)