#2 is higher than I've seen on lists about "toughest NFL venues" before but #1 is the Ravens? That's a new one.
They're basing it off this: "Since 2003, the Seahawks have outscored opponents by 430 points at home. On the road, they have been outscored by 361. That differential (791 points) is the league's second-biggest gap, after the Baltimore Ravens."