Yes it is... and that contract (agreement between all the players collectively and the NFL) granted Goodell the power to be "Judge, Jury, and Executioner".

That is the problem... Had the very players that are claiming he does not have that power not given it to him, they would have a legal case. So far there is no breach of contract, only an execution of powers granted.

At this point, all they can pursue with any realistic expectation of success are personal cases for slander and deformation of character.