Look up history, law doesn't mean its right.Contract law is called that... because it is law.
...and the contract that the NFL players association has signed with the NFL states that contracts are not guaranteed unless there is specified guaranteed money... and X didn't sign a contract with that. Therefore... he can be cut.
Thems the rules as currently constituted. Feel free to say they should be changed.
Then people should not start Boston tea party, and should not start Franch revolution, its all against the law. Law allowed slavery before civil war.
Law 101. Go learn it.