When I had an ostomy I used a band with a pocket for the bag. I ordered it from ostomoysecrets.com although there are other brands. I would use a belt for extra security sometimes too. Also for your games and practices, I would suggest looking into a closed-end bag that had a filter - they're only one use but they hold more output, spread it out more evenly so it doesn't bulge so much, and the filter will release the gas that comes out too... Because you know how sports are good at getting us cleaned out
Also when you are sweating a lot just be on the lookout for yeast infections around the stoma.
Expect to have some frustrating moments figuring it out, but I think you'll be pleased to discover that the ostomy really isn't inhibiting- and if you're like most of us, it actually gives you more freedom now that your bowels are under control
Best wishes!