I found some of the SportBetting sites that claim to be decentralized and purely Player vs Player. I have tried some of them, and I could say that their system are not really good, even if you check their website now, it is not updated anymore. The last update are mostly from match last year. Moreover, their support are not that good either, so there are some, but not recommended.
Did you tried our app Kryptium? We are really interested to get feedback from users. Please note that Kryptium isn't a site(Web application) but a desktop application available on Windows, Linux and Mac OS. It works similar to Desktop crypto wallets and currently has deployed smart contract on Ethereum, Ellaism, Callisto, Ethereum Ropsten and Rinkeby testnets. So it's possible to try the application on testnets using currencies with zero fiat value.