A contract is subject to the employer and the person signing, any clause can be added in as long as both parties are happy. I work with contracts for a living trust me it can be done and if there was a coaches clause incorporated in the contract he could get out quite easily.
It’s pretty simple really. The player signed a 2 year contract. The contract is to play at the club, not under a certain coach. Mernda are in their rights to hold the player. Unfortunately Roxy don’t have a leg to stand on at appeal. They are much better to try and negotiate something with the other club