Like Jay (and the experts) I don't think this is a credible threat (odds are against terrorists getting 7 dirty bombs, much less one to an NFL stadium. But there is a possibility thanks to the ACLU.
As Jay writes:
Well, that isn’t exactly true. Thanks to the a lawsuit from the ACLU, Tampa’s Raymond James Studio were forced to stop all their searches. The ACLU also filed suit against the 49′rs to do halt their searches as well. I’m not sure if that case is settled or not. Surprising that they are not on the list being how easy the ACLU made it for them in Tampa. Hopefully the FBI’s scepticism is right and there is nothing to worry about. Still, threats like this highlight why security proceedures at these kind of events are so important, and why groups like the ACLU fighting against them is so dangerous
He's referring to the security at NFL staduims after the ACLU got through with them, it's very scary to someone that has been and will go again to an NFL game.