This week features the top 2 teams in the NFC West facing off in a high-stakes game. It's a must win if the Seahawks are to have any hope of taking the top spot and not find themselves fighting for the Wild Card. Despite its significance in terms of playoffs, the San Fran/Seattle rivalry provides enough drama for the match up on its own. Although Wilson does have the rivalry advantage with a 11-3 record - featuring a tough 26-23 loss the last time they played, this may very well be the most complete San Francisco team the Hawks have faced since 2012.

As a group, the 49ers' opponents are 22-43 — having won just 33% of their 65 combined games through week 9. While demolishing some opponents such as the Carolina Panthers, a 28-25 thriller against Arizona was, by general consensus, disconcertingly close. For the moment I would like to focus on the defense of the 49ers, as the Seahawks offense will have to find a way to unlock it if they are to have a chance.

The most amazing thing about the 49ers in 2019 is their performance on third down. The team have held opponents to a conversion completion of 27.5%, nearly 12 percent lower than the average of 39.1%. If you exclude the statistical anomaly of the Mudbowl 9-0 win against Washington, the 49ers have allowed 4/31 on third down in the last 3 (normal) games.

Few can deny the thought that the NFC runs through San Francisco this year.

An 8-0 record is the result of a defense ranked third in points while also sitting first and seventh for yards, defense. The opportunistic defense clocks in at 16 turnovers, good enough for fourth in the NFL. While they dominate the passing attack, the relative weakness appears to lie in the run game - ranking 22nd in all teams for yards per rushing attempt. This appears to be a discrepancy when you realize that the 49ers have 30 sacks, 3rd most in the league.

The 49ers play a system that overwhelmingly uses Cover 3. It's the bread and butter of the defense and is definitely worth a look. Before we dig into the 49ers specifically, we need to understand the Cover 3 in general.

So how does it work?

As the name suggests, the defining trait is the three deep defending zones roughly 10-15 yards the line of scrimmage. In the 49ers' system, that will leave four underneath zones and four rushing players.

It is of common belief that Cover 3 is the fewest number of deep zones you can comfortably defend the deep ball with. As such, it is a lot weaker than the now dwindling Cover 2 in underneath, intermediate, and short passing areas. The formation has a long history as a fringe option along with rotations such as Cover 4 or zone blitzes. Its role of deep middle protection was more often filled by the iconic Tampa 2 which sunk a linebacker deep into the weakest part of the deep area.

Over time, league changes and tendency evolution drew more attention to the Cover 3 as the basis for an entire scheme and became the buzzword after the 2013 Seahawks found great success with a modified Cover 3. As the passing league developed and the deep ball became the NFL's signature play, Cover 3 saw increased usage to slow the long bomb.

As for the four underneath zones, they are split across horizontally and most schemes will place them at even depth. Some schemes have been known to drop the corners back slightly or move them closer to the line-of-scrimmage. The real deliberation of the underneath portion is due to personnel. If you have four defensive backs, using three deep zones with one shallower, teams start to struggle?

Variations of Cover 3.

Cover 3 sky. The 3 deep zones are taken by the outside corners and the middle safety. The strong safety must take the responsibilities of an outside zone underneath. Has to be the one closest to the boundary. Cover 3 Buzz. 3 deep zones are the 2 outside corners and the middle safety again, but this time the Strong safety takes an inside underneath zone. This is the one that Seattle used extensively in 2013. Cover 3 Cloud. 3 deep zones utilize both safeties and one outside corner. The last corners position is flexible so he can drop into one of the outsides underneath zones or can be used to go into man with the guy opposite. He can also take a really shallow outside zone in case of crosses, screens, drags, and curls. It can also be really useful in run support to immediately shore up an edge and make the runner turn back towards to middle of the field and back into the jaws of the defense... Figuratively. Cover 3 blitz. Simple. In buzz and sky, the strong safety will line up wherever (up next to the free safety, down by the slot, roving the middle with the LBs) and he will attack the gap opened by the D-Line. In cloud, a cornerback will blitz. While a LB or slot corner can do this, the unassigned DB has to fill their zone.

The 49ers will use every single variation of cover 3 to change the weaknesses to strengths and throw off the opposition.

Now that we know what it is, let's look at how it works and how it can be beaten.

Key points of cover 3:

Much stronger against deep throws. Not in situations such as four verts, with four go routes but this is normally unlikely or anticipated. Some cases very weak to short horizontal passes.

As corners bail deep and linebackers drop into position to cover intermediate throws, soft edges emerge. Occasionally partially negated in cloud. Easily spotted as corners take 5-7 yards off to shorten time to zone. No use defending deep if the other guy gets there first.

Two inside underneath zones means at least six in the box. Likely seven or eight in an expanded box or tightened formations with lots of TEs. Middle runs can be well defended if the line and backers are good. In buzz and sky, safety can also get involved.

This is a very rough approximation of the cover 3. The orange dot is a marker to show how the zones would be played if the ball was placed here. The blue are the deep zones, yellow are the underneath and the red circles are the weaknesses of the Route. The deep intermediate Seams are the most vulnerable and, if you see a slot receiver or tight-end get vertical immediately, it is designed to attack this very seam. Verts and HOSS concepts are very effective at targeting these weak-spots.

With what we call the 2nd (linebackers) and 3rd (defensive backs) levels talked about, let's discuss the importance of the defensive line. In the usual cover 3, you will have 4 rushers independent of the other 2 units so they are free to run Stunts, crashes, and alignments however they so please. However, despite their independence from the rest of the team in terms of play to play adjustments, the defensive line plays a crucial role in both the pass and run defense.

The Pass

The job of any d-line when playing against the pass is to put pressure on the quarterback and disrupt the throw. As shown above in the weaknesses of Cover 3, the shallow flats can be exploited as the corners sink deep and the linebackers are unable to get to the edge quickly. To avoid this, defensive ends will attempt to use a speed rush to get to the outside of the tackle and actually block the passing lane to the flat. A good example of this is Nick Bosa's interception. Here is an Imgur album detailing that exact interception. Aside from this, the job is to create suffocating pressure and not allow enough time for scramble drills where everybody runs into random zones and the coverage all breaks down.

The Run

The job in the run game is to stay disciplined and not play hero-ball. For anybody who doesn't know, hero-ball is a phrase, popular with coaches and film watchers, for a player who will try to be the hero and come of his assignment to attempt a high risk tackle, lateral the ball, or try an on-the-run crazy throw. Other examples are jumping a route for an interception and generally charging into boom or bust plays. It is the bane of a perfect game-plan and the savior of a terrible one. Bill Bellichick HATES hero-ball, while the play-style wrote Mike McCarthy's checks for years.

If a player attempts to shoot a gap and get a tackle for a loss but misses, he automatically creates a running lane where a player is supposed to be holding the block and not supplying breathing room.

Cover 3 has 6-8 men in the box so there is no need to go for broke because, if you hold gaps correctly, there is nowhere for the Running back to go. The run slows. A player sheds his block and engages the slowed running back while the linebackers pour in to make sure if there is a missed tackle, no opportunities are created. The job of the D-line is to seal off any easy lanes, make a tackle if the player tries to force his way through, and let the linebackers clean up the rest.

So How Do The 49ers Execute and Change this Gameplan?

The 49ers are deadly effective in cover 3. As a deep defending concept, they are much more likely to give up the short pass or run, rather than the deep ball.

This is by design.

When a team finds themselves in a negative games script, they tend to abandon the run and look to move the ball in chunk yardage through the air. Because of this, if the 49ers have the lead, the opponents tend to play straight into the strengths of this 49er defense - eliminating the deep ball.

Essentially, teams get desperate when the 49ers gain a lead and begin forcing deep routes. The better the offense, the better the defense. Even in close scenarios, the cover 3 makes teams work hard for every yard. Eventually the short passing, screen, and running game can frustrate an offense if they are proving ineffective due to the athletic defensive line, good position, and solid tackling defense. A coordinator will start to dial up longer throws with higher risks - feeding into the 49ers strengths.

For example, to stop the weak zones from being exploited down the deep middle, the inside linebackers would carry the receivers up the field to stop a potential passing lane. To exploit this, several teams use what is known as the Ohio concept. The Ohio concept uses a streak route inside to clear out the intermediate middle while the outside receiver runs a 5 or 7 yard in-route into the vacated hole.

Another important aspect is play action is that linebackers tend to aggressively play the run and open up the zones between the intermediate and deep zones. Again, this is only applicable where a run is expected so, when down in crucial situations, this is not applicable as the linebackers will play the pass rather than the unlikely play action.

Sherman will occasionally help in run support while playing his deep zone responsibility by starting down by the line of scrimmage - much like the iconic Seattle Cover 3. The other corners and defensive backs are unable to completely hide the tip offs for cover 3 as they are not familiar with this particular style.

The cardinals, right until the end, very notably stayed with the short passing game and allowed yards after catch to be the primary force. The week before, in Carolina, the Panthers threw seven deep balls, with one being caught... caught by Richard Sherman for an interception. Five of these balls came in the 2nd half. Carolina did have a 20 yard gain from a pass but that was Allens best of the day in terms of air yardage.

They only threw 3 deep balls all game with one of them in the second half resulting in a masterclass 88-yard touchdown. The play occurred in a rare man coverage.

Conclusion

Though individually the San Francisco defense is highly talented, the strength of the offense and the scheming must be commended.

They are very much a complete team.

The opponent has never led in 50% of their games and find themselves constantly chasing the lead. Additionally, only one team has scored more than once against the 49ers in the 4th quarter. The explosive offense sets up a terrifying defense who are designed to not give up the big play.

You can win against the 49ers, as the Cardinals nearly did, because they played to the weaknesses of the defense, instead of trying to outplay strength to strength. Expect Carson to have a big receiving day, short passes often, and an insistence on the run game. Even if you don't believe the ground game create success, make a note of how many players are committing to the run, and look out for long play action gains if the ground game is stifled.