Make it like a salesman's commission. You win, you get paid. Have it tiered. Ranked wins, big wins, worth more than the low-end games that you're expected to win. Oh sure, there could be a base salary extended so a coach could pay the bills, feed the family, etc. However, results on the field then directly lead to more compensation. Come to think of it, that's how pro athletes and coaches/managers should be paid as well.