Technically the Constitutional protections of geography were included in the ratification of the constitution in 1789. Additional protections were added when the 14th amendment was ratified.
The only question in this case would be whether the use of the Government owned and operated stadium by the Seahawks would require that the Seahawks provide the same protections to out of state visitors that would apply if the government itself were selling the tickets.
In this case since the rights of the Seahawks are in the form of a leaseholder to the seats, any sale of tickets would be in the form of a sub lease of government property and as such, the Seahawks would be held to the same standard that would apply to the State.
Since the State could not so flagrantly discriminate against the Citizens of California, the leaseholder to State property cannot do so either.
That is utter nonsense. Absent some provision in their lease agreement requiring the Seahawks to sell to all comers, there is no requirement to do so. Private companies do not become quasi-governmental entities simply because they lease public property.
I'm shocked that Freepers would support forcing a private company to sell their product to customers the company does not want to serve. Particularly where the compnay could make a strong argument that doing so would harm the company (stadium loudness/etc. has become a significant part of the Seahawks brand).