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The Seahawks’ defense has no weakness, so the Broncos must create one. The best way to do that is to align in a 3 x 1 formation with wide receivers Demaryius Thomas, Eric Decker and Wes Welker all to one side and tight end Julius Thomas alone on the other. (In football jargon, this would make Julius Thomas the “X-iso”; see image below.)
All season the Broncos have featured this formation prominently in the red zone. Super Bowl XLVIII will be determined largely by what happens when they use it not just there, but also throughout the rest of the field. If the Seahawks match personnel and put cornerbacks Richard Sherman, Byron Maxwell and Walter Thurmond to the three-receiver side, either Kam Chancellor or K.J. Wright will be left outside against Julius Thomas. There’s your weakness. While Chancellor is an excellent strong safety and Wright is a superb outside linebacker, neither is a good press-man cornerback—at least not against someone like Julius Thomas, who is a limber 6-5, 250 pounds, angular and explosive in confined movement. Peyton Manning would eagerly attack this matchup, and it’s almost guaranteed to be one-on-one considering free safety Earl Thomas aligns in centerfield on virtually every down. And if the Pro Bowl safety were inclined to rotate early to a particular side, he would have three reasons—Welker, Decker and Demaryius Thomas—to choose the side away from Julius Thomas.
But it doesn’t necessarily have to be a 3 x 1 set. In the AFC Championship Game, Manning completed a crucial 37-yarder to Julius Thomas from a wide-split alignment out of a 2 x 2 set, with Wes Welker in the slot (see image below). Against man coverage, this set came with linebacker Jamie Collins (who, it’s worth noting, is a better athlete than Wright ... and in terms of movement skills is actually comparable to Chancellor) getting beat.
The Seahawks didn’t see trips receiver 3 x 1 formations too often this season, but when they did they generally matched corners on wideouts only in obvious passing situations. When facing the look on first or second down, they typically stayed in their base press-Cover 3. This includes when it’s a trips receiver 3 x 1 closed formation, which means Thomas, instead of playing X-iso, is aligned in his usual tight end spot along the line of scrimmage.
If the Seahawks play base against these looks on Sunday, then either left corner Sherman or right corner Maxwell will be on Julius Thomas. In this case, the Broncos would create a weakness for the Seahawks on the strong side. Most likely, Thomas would align on Sherman’s side so that Manning could work the side opposite the league’s best cornerback. Doing that would make Sherman a nonfactor and give Manning three wideouts against two corners. The Seahawks would be in zone, so Manning wouldn’t necessarily be trying to simply locate whichever receiver isn’t facing a corner. Instead, he’d be evaluating specific zone-beater route combinations. He’d also have a full arsenal of receiver screens to choose from, as his two best screen-catching wideouts, Welker and Demaryius Thomas, would be close together. That creates opportunities for screens, both real and fake.
This is the beauty of an overloaded trips 3 x 1 set: beyond creating favorable matchups, it forces the defense to reveal its coverage before the snap (particularly when the defense runs a straightforward, execution-based scheme like Seattle does). If all of the corners follow the receivers to the strong side, it almost always means the D is playing man. If the No. 1 and 2 corners stay in their usual outside spots, it means zone. Manning is tough enough as it is; when he can diagnose the coverage beforehand, he’s all but unstoppable.