If you have ever wondered what clauses are included in a standard NFL contract, the current NFL CBA has an example found in Appendix A.
Within that 25-section contract, you will find the following verbiage in Section 11 regarding Skill, Performance, and Conduct:
Player understands that he is competing with other players for a position on Club’s roster within the applicable player limits. If at any time, in the sole judgment of Club, Player’s skill or performance has been unsatisfactory as compared with that of other players competing for positions on Club’s roster, or if Player has engaged in personal conduct reasonably judged by Club to adversely affect or reflect on Club, then Club may terminate this contract.