Seattle has a sound philosophy, and they draft players that fit that philosophy. They identified Thomas and Chancellor - ideal compliments at S. They had Chris Clemons and Bruce Irving, but they bring in Avril and Bennett. Unlike teams that just say it, they actually believe you can never have too many quality pass rushers, and it shows. They draft another big CB just about every season. They already had Lynch, but they drafted 220+lb RB's in each of the last two drafts (who are both very good). Miami could have drafted Turbin, btw, but chose Miller. They have clear visions for both sides of the ball, and they're excellent at finding players that fit that vision. After almost every Seattle draft (the one with Earl Thomas being the exception), most analysts give them something like a B- and talk about the confusing picks. They built their D to effect QB play - while sacrificing a little (very little run D). They're able to do this in large part because of Sherman and Thomas. While they may not be built to stop the run with their front 7 like SF, when you drop Chancellor into the box as the 8th man, they're about as tough as anyone, but that unit is built to be the best pas D in the league (pass rushers, CB's, tall, athletic LB's, and all-world S's). It's why they're able to stifle Brees one week and shut down Gore then next.
On offense, they play like they trust their D - as they should. During the SF/SEA game, I told my GF that a punt was a wash (especially early) - rather than a win for the D. Seattle racks up carries for Lynch, and even the great D's begin to show cracks come the 3rd and 4th quarters. Combine that with a QB who doesn't mind throwing after handing the ball off 5+ straight times and has the ability to make big plays. During the Denver/NE game, Simms mentioned that the Broncos felt they lost to NE during the regular season, because they ran the ball too much and lost the rhythm in their passing game. Never heard Wilson complain about this issue.
So you have a clear vision that translates to sustainable success, and you're good at identifying the players that fit that vision. It doesn't sound hard, but there's only one Seattle in the NFL.
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I actually didn't think Seattle would be THIS good this season, but I still picked them to win the SB, because they match up so well with the top tier teams. That pass D is a trump card, and the running game is a will tester. The only difficult match up (on paper) is SF.