I'm a 49ers fan and I live in Montana, so I see a lot of Seahawks games as they're the local NFC team.
What their secondary will do is grab the jersey of a WR after 5 yards to direct the WR where they want him to go (Sherman does it a lot). Honestly, I don't have a problem with it because the defense is already at a disadvantage due to the offense knowing the play they called and then the NFL swung the pendulum in favor of the offense with all of the stupid ass rule changes.
To beat Seattle, you have to be physical with them. They're going to try to out muscle you, you have to be able to fight back. Take the game that SF won this year against them, SF was taking it to the Seahawks and won the game due to Gore's 40yd run to setup the game winning FG. If you're not prepared to be physical with them (like Denver was last night), you're going to get destroyed.
I knew that game was over last night once Seattle made it a two score game. If they force you into a situation where you have to pass to catch up, it's lights out.