There is only one rule, get your c-shirt and love the game! For general rules open this page and for specific Tournament's rules and rewards check each Tournament page.
You can win ETH every time your Tournament C-shirt's team scores a winning in its championship, and in many more ways, check the rules & rewards for each Tournament.
You can secure a spot for yourself in the whitelist to enter the the private sale of 800 C-Shirts (free-mint), and you can mint how many C-shirt you want in the public sale.
Every C-Shirt gives you lifetime access to free minting of 250 Tournament C-Shirts for each championship, gives you airdrops of new Tournament C-Shirts and voting power over what sports championship you would like to see in the next year.
You can get Tournament C-Shirts by private sale (free-mint) if you own a C-Shirt or public sale if you don't or missed the private sale.
You can also find both the C-Shirts and Tournament C-Shirts on Opensea.