In the New England Patriots' two biggest games of the season, they enter with an advantage.
Because they are so stout against the run, their defense is built perfectly to shut down offenses such as their previous opponent's, the Houston Texans', and their upcoming opponent's, the San Francisco 49ers'.
The Patriots are playing better defense recently, but they're not without their weaknesses. That being said, the 49ers offense is a house of cards built on its ability to run the ball. Taking away that foundation could cause the whole thing to crumble.
The 49ers rank second in the NFL in rushing and have the seventh-most rush attempts. They also really love the play-action passing game; 49ers quarterback Colin Kaepernick uses play action on 34.8 percent of his drop-backs, while Alex Smith's play-action percentage was 22.7 (via ProFootballFocus.com).
Those heavy tendencies will allow the Patriots linebackers to attack the backfield much like they did against the Texans, employing the mentality of stopping the run on the way to the quarterback.
That certainly seemed to be the mentality when Patriots linebacker Dont'a Hightower tackled Texans running back Arian Foster for a three-yard loss early in Monday night's blowout.
The Texans tried to run up the middle out of the 21 personnel grouping—two backs, one tight end, two receivers. The Patriots sent the kitchen sink at the line of scrimmage, with only four defenders in coverage and seven at the line.
That being said, they were ready for anything.
The safeties stayed deep, while linebacker Jerod Mayo came clean off the left side to pressure Texans quarterback Matt Schaub in the event of a play-action pass. That was deemed unnecessary when Foster took the handoff, and Hightower did a great job of penetrating the B-gap and manhandling fullback James Casey.
Recently, the Patriots linebackers have attacked the line of scrimmage a lot more frequently, possibly due in part to their struggles in coverage. That could become a problem if the 49ers are able to expose the middle of the field.
We have already seen the Patriots linebackers get exposed in coverage this year (more on that later), and the 49ers have been good at getting linebackers to play over-aggressive against the run, opening things up for the passing game, specifically in play-action passing situations.
Here, almost the entire Dolphins defense bites on the play-action; that includes defensive end Derrick Shelby, who loses containment, allowing Kaepernick to roll to his right.
Among the "biters" is linebacker Koa Misi; the pivot route by 49ers receiver Michael Crabtree catches Misi off-guard, and the linebacker is in no man's land from that point.
This play went to Crabtree, but tight end Vernon Davis should also be in focus for the Patriots defense. Davis has not been as central to the offensive game plan as in year's past (38 receptions ranks third on the team), but he's just as explosive and just as much of a threat to score.
That being said, the Patriots could call on safety Tavon Wilson to cover Davis if the linebackers are unable to do so or are too busy blitzing and defending the run. Wilson was drafted specifically for this reason: his ability to cover tight ends well, while not giving up too much against the run.
They should try something different, at least when it comes to covering tight ends. The Patriots have been burned by tight ends this year, and rank 31st in coverage against tight ends, according to Football Outsiders.
What would you expect? The Patriots linebackers aren't exactly the leanest, quickest or most athletic group of guys, with each standing at over 6'2" and weighing an average of 248 pounds. They are built to stop the run: the Patriots know it, and their opponents know it. Thus, we have seen teams attack the linebackers in coverage all year, and have seen the linebackers attacking the line of scrimmage a lot more recently.
Seahawks tight end Zach Miller was able to expose Patriots linebacker Brandon Spikes' lack of athleticism on a seam route in the first quarter of Seattle's upset win.
With quarterback Russell Wilson in the shotgun, the Seahawks spread out the Patriots defense with three wide receivers. New England responded with a nickel defense of four linemen, two linebackers and five defensive backs, with Patrick Chung as the lone deep safety.
Once Wilson saw Spikes in man coverage, he knew where he was going with the ball, hardly even trying to fool Chung as he stared down his target.
He put it up high where his athletic tight end could get it, and where Spikes couldn't.
That's just one example of the Patriots linebackers being exposed in coverage, but it's happened quite a bit this year. Bills tight end Scott Chandler had five catches for 65 yards and a touchdown against New England in Week 9. Colts tight end Dwayne Allen had six catches for 69 yards.
Of course, both of those performances came in Patriots victories, so while the Patriots may be giving up yards and catches to tight ends, they're certainly not getting defeated by them.
Run defense and discipline against the play-action passing game will be key, but one of the most important keys could be to keep containment on Kaepernick.
The Dolphins were able to hold the 49ers to six first-half points largely through their ability to prevent him from scrambling all over the field (he had zero rushes in the first half).
Their gap discipline even led to some pressure on a couple of their sacks, including this one from Dolphins defensive end Jared Odrick, who lined up at defensive tackle on this down. ProFootballFocus.com grades Odrick at 0.3 against the run (ranks 37th among 4-3 defensive ends) but at minus-20.3 as a pass-rusher (61st).
Defensive end Cameron Wake and linebacker Kevin Burnett both had outside leverage, and the line as a whole maintained the gaps well, which prevented Kaepernick from getting outside the pocket or scrambling. That, coupled with solid coverage downfield, resulted in the sack.
Gap containment was a key against the Texans, but for different reasons. Remember the huge game from defensive tackle Vince Wilfork? He did a lot of his damage by penetrating the backfield, registering one sack, two pressures, three tackles and four run stops, according to ProFootballFocus.com.
The Texans had two huge outside runs to start the game, with the first being called back on an illegal formation penalty. On their first try up the middle, though, they found out what a wrecking ball Wilfork can be.
Even while being thrown to the ground, Wilfork was able to make the tackle on Texans running back Arian Foster.
The Patriots were able to make the Texans one-dimensional by taking away the running game, holding Houston to just 42 rushing yards on 13 attempts (3.2 YPA) in the first half on their way to a 21-0 halftime lead.
A similar performance against San Francisco's running game this week could help the Patriots build another early lead.
The 49ers offense isn't one-dimensional, to be sure, but the key ingredient for them is a productive running game. The Patriots could make the 49ers incredibly one-dimensional if they're able to take it away, and they have the tools to do it.
Erik Frenz is the AFC East lead blogger for Bleacher Report. Be sure to follow Erik on Twitter and "like" the AFC East blog on Facebook to keep up with all the updates. Unless specified otherwise, all quotes are obtained firsthand or via team press releases.