Whom did ErisX believe would be the counterparty to a football future if retail was not allowed to trade them?
This is something I've been looking for ways to do for quite some time, and I haven't find a good option other than PropSwap - would be a really neat feature for Fanduel/Draftkings to add, considering the volume they're getting now.
There are bet exchanges, like betfair, which are pretty much what you are looking for