I think you cleared everything up, thanks. I wasn't thinking about the commission being split between all the investors.

Maybe consider holding player balances to 1 or 2 extra decimal places. If I refer a play who makes a million bets of 1k satoshis each, the way things currently stand I get nothing at all for it. Each bet earns me 0.5 satoshis, which is rounded down to 0. If you added up all the half-satoshis, I'd end up with 500k satoshis, or 0.005 BTC.

Nobody minds losing half a satoshi, but losing a million half satoshis is a different matter.