Seattle's defense ranked only 11th in overall third-down conversion rate (35.3 percent), but allowed a league-low 4.1 yards per play on third down. In the playoffs, the Seahawks have allowed only 6 of 23 third downs (26.1 percent) to be converted and the longest conversion was on a third-and-5.
Nearly 80 percent of third-down plays are passes in the NFL, so this matchup heavily relies on Manning's pre-snap reads against a defense that rarely blitzes overall -- 64.9 percent of third-down pass plays saw the Seahawks rush three or four defenders -- but can blitz effectively.
On third down, Seattle has allowed the fewest touchdown passes (two) and intercepted the most passes (12), however it must be noted that Carson Palmer was responsible for five of those 12 interceptions. On third down, Manning's thrown a league-best 14 touchdown passes and including the playoffs has converted 47.3 percent of his attempts.
Seattle was able to put the quarterback under duress on 38.5 percent of third-down pass plays, including 20 sacks. Manning's been sacked on seven of his third downs and put under duress only 20.1 percent of the time (converts 21.2 percent of plays when pressured). Pressure is a must, because Manning's four primary receivers each have 31-40 targets on third down, so he'll sit back and make the open guy his weapon of choice -- regardless of who it is. That's why Manning will gladly let Richard Sherman, who primarily plays on the defense's left side of the field, lock up one receiver. He has numerous options and no favorites.
If the weather conditions are really poor, Denver may find running the ball on third down to be both a necessity and an advantage. Seattle ranks only 17th in third-down run defense DVOA and 19th in conversion rate (53.3 percent). Excluding a kneel down, Seattle faced 44 runs on third down in the regular season. Seventeen of the runs were by a quarterback and a dozen were scrambles. That's never a concern with Manning. When the Broncos run, attacking the right end should be the plan. Seattle's defensive line ranks 24th in Adjusted Line Yards (explained here) on runs to the right end while Denver's offense ranks seventh on those runs.
One of Denver's best plays against New England was Manning's audible to a run on third-and-10 that produced a 28-yard gain to the right by Knowshon Moreno. While Manning is unlikely to get away with another "Montana Fat Man!" audible for that draw, he can just change the name to something else this time. His willingness to let the running game do the dirty work against this great pass defense is one of the biggest factors to Denver's success.
If Manning's forced into a lot of third-and-long situations (needing 8-plus yards for a first down), he has been very impressive, converting 27 of 70 plays (38.6 percent). But Seattle leads the league there, allowing only 2.9 yards per play and a 14.5 percent conversion rate on third-and-long passes. If we include the playoffs and look when it gets to third-and-11 or worse, quarterbacks converted once out of 39 plays (2.6 percent) against Seattle.
However, it was just one season ago when the Seahawks' defense ranked dead last in the league on third-and-long, allowing a league-worst 36.4 percent conversion rate and 32 first downs. Things can change quickly in the NFL. Just ask the Broncos.
Seattle offense versus Denver defense