work contracts are different than profesional or said sports contracts... lets say i sign a contract with x to play for 4 years, lets asume there is no clause about playing and x amount of games or ani other condition to allow 1 side to finish the deal.. that leaves only 2 options for contract termination, 1 expiration date, 2 mutual agreedment of premature termination, any other reason would be a violation of the contract wich points us to the "infraction fee" inside of said contract (if agreed to) OR the general sanction from the general LAW of said country...
having said that , EVERTON or any club doesnt "allow " nothing, those are the rules of a contract, if you want it terminated early, you PAY.