The NFL is a commercial entity that conducts interstate commerce. The Constitution specifically enumerates Congress with the authority to regulate commerce between the states.
(Article I, Section 8, Clause 3). The clause states that the United States Congress shall have power “To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes.”
The commerce clause was intended to prevent one state from taxing products from other states passing through...any other interpretation is treasonous IMHO.