I can't speak to pat downs or metal detectors at the stadium as I haven't been there myself.
However I will give you this from the WA-CCW email group
" In attending a recent seahawks game the
security people were patting everyone down on entry. (no I wasn't
carrying) but if I were on my hip it wouldn't be very concealed at
that point. The tickets that we had nowhere on the ticket did it
state "no weapons" but it did say ejection for failure to comply
with any "security policy""
The problem is that while Seahawk Stadium is a public facility and as such the state premeption should apply and bar them from prohibiting concelaed carry the stadium is un fact leased or in some other legal manner given to First and Goal to run and this means the private property exemption to state premption applies.
You're really in untested waters here, but AFAIK the worst they can do is ask you to leave the premises if you comply it's all good except you are out of the staduim, the real trouble for you would be if you refuse to comply with their order to leave.
I'm not a lawyer, I don't play one on TV, I've bnever even seen a concert truck.