Even if front loaded contracts aren't technically permitted in the NFL usually when you see a big 4 or 5 year contract get signed only the first 2 to 3 years of the contract will be guaranteed money. That way a team can cut that player without taking a cap penalty for doing so. They at least need to come up with a system to decide how much of a contract is guaranteed and how that guaranteed money is distributed. That's always one of the main points they bring up when a new contract is signed in the NFL is how much of it is guaranteed.