I am a CPA weighing in here.
I am not your CPA, I am not a professional athlete's CPA, I am not offering tax advice.
Athletes in states with state income taxes will be asked to defend their position and it will likely come down to their individual contracts.
NIL is not for playing football, but they will likely go to court and try to determine whether that is true in substance and in form.
There's a lot of half-truths in this thread (SALT cap limitations for federal taxes, 51% residency requirements, etc) that are not 100% accurate or there are workarounds that are tried and true.
I will just offer my opinion that state taxation makes a huge difference and that even if someone is able to make the argument that X percent of their income does not apply to a state that has state income tax, you still have to pay the legal fees and CPA firm fees (along with potential penalties if you lose) if you are the first one taking an Uncertain Tax Position in that state.