I know what you're thinking. Knowshon Moreno, really? Peyton Manning for sure has the most important role on the field in this game, but thinking a little deeper proves that Moreno will be the X-factor. This can be reasoned because of the weather and things seen in Seattle's defense.
The Seahawks statistically have the best pass defense in the NFL, holding opponents to only 172 yards passing per game. They also have the seventh-best rush defense, but running the ball is still the smarter way to go in this one. Moreno will get more carries because of Seattle's elite secondary.
Seattle's back four is loaded: Richard Sherman, Kam Chancellor, Earl Thomas and Byron Maxwell. Sherman, Chancellor and Thomas are among the top defenders in the league. In NFL.com's Top 100 Players of 2013 list, both Sherman and Thomas were mentioned. When next year's list comes out, it's likely that Chancellor will be on there as well.
All of that said about Seattle's defense should make it clear that for Denver to have success in this game, the Broncos will need to establish the running game early. Throwing on Seattle is going to be tough, but if Moreno gets going early, they can take advantage of play-action passes.
The weather will also have an impact on the amount of run plays by Denver. In colder weather, it's likely that Manning and Co. will attempt to get a ground game going because of the difficulty to throw in bad weather conditions.
In a game earlier in the season against New England, Manning and the Broncos faced very cold weather. The game plan for that matchup was feeding Moreno the ball; he had 37 carries in that contest, going for 224 yards. Moreno only eclipsed 20 or more carries in two other games this season.
I think the game plan for the Super Bowl will be similar to the New England game. John Fox even said he feels that Moreno will be a big part of the game plan, per NFL: AroundTheLeague:
Seattle's Run Defense
Although the Seahawks' run defense has been solid for the most part, in the playoffs teams have had success on the ground.
The New Orleans Saints rushed for 108 yards in their playoff matchup. In the NFC Championship, San Francisco was able to pick up 161 yards on the ground. Of course 130 of those yards belonged to Colin Kaepernick, but they still show an opportunity for Denver to capitalize in the run game.
Moreno is also effective as a receiver out of the backfield. He had 60 catches for 548 yards and three touchdowns receiving this season to go along with 1,038 yards and 10 touchdowns rushing.
The weather and Seattle's top pass defense will allow Moreno to have a big game. He may not go for 224 yards in this game like against New England, but I think he sees his carries go up from the previous two playoff games. His increased rush attempts will make Manning even more dangerous off the play-action and halfback screen plays. An even more dangerous Peyton Manning is certainly not what the Seahawks want in Super Bowl XLVIII.