Credit: NFL Game Rewind

In today's installment of the "NFL 101" series, former NFL defensive back Matt Bowen breaks down the basics of Cover 3 to give you a better understanding of the game.

Click here for a breakdown of Cover 1.

Click here for a breakdown of Cover 2.

Cover 3 is a three-deep, four-under zone defense run out of both base and sub-package personnel at the NFL level.

A scheme that shows up often in early down-and-distance situations to create an eight-man front, Cover 3 is a first-day-install defense.

In the standard three-deep zone shell (rush four, drop seven), both cornerbacks drop to the outside third with the free safety playing the deep middle of the field (or middle third).

Underneath, the strong safety and open-side linebacker (or nickel) play the curl-flat drops with two linebackers sinking to the middle hook drops inside.

Otto Greule Jr/Getty Images

Often thought of as a "high school" defense due to the quarterback's ability to target the secondary with three-level concepts and inside seam routes, the Seattle Seahawks proved otherwise this past season as they leaned on the zone scheme as one of their core coverages on the way to a Super Bowl championship.

Let's break down Cover 3, 3 Buzz and 3 "Cloud" while taking a look at the Seahawks' three-deep technique at the cornerback position.

Base Cover 3 Alignments and Zone Drops

NFL defenses will show Cover 3 out of their base fronts to walk the strong safety down as the primary force/contain player in the run game versus these offensive personnel groupings:

Regular/21 (2WR-1TE-2RB)

Ace/12 (2WR-2TE-1RB)

Tank/22 (1WR-2TE-2RB)

Heavy/13 (1WR-3TE-1RB)

Using the All-22 coaches tape, check out the Panthers' 4-3 front in their Cover 3 pre-snap alignment versus the Rams' Regular/21 personnel in a Pro "I" formation.

Credit: NFL Game Rewind

In Cover 3, the cornerbacks can align off at a depth of seven to eight yards or use a "press-bail" technique (align in press, open and sink) to get to the deep outside third.

Here, both of the Panthers' cornerbacks are in a press-look and will use a "bail" technique to sink before the snap (create a cushion versus the wide receiver). The corners are responsible for playing any vertical concepts (split two verticals to the same side of the field) and must funnel the deep inside breaking routes (dig, post, etc.) to the free safety.

The free safety's technique/drop is very similar to Cover 1. He must gain depth to create a downhill, 45-degree angle to the post or dig with the ability to get to the bottom of the numbers versus the outside 9 route.

In this example, the free safety aligns in the deep middle of the field, but NFL defenses will often roll from a two-deep look to disguise Cover 3.

The curl-flat defenders (strong safety and Will 'backer in this example) read their run/pass keys (tight end, open side tackle) and drop to a depth of 10-12 yards to the top of the numbers.

They are taught to buzz through (or hold off) the curl (sink into throwing lane) and widen with the flat. Curl-flat defenders cannot get out-leveraged to the flat and must run with the wheel route from the No. 2 receiver.

The middle hook defenders (Mike and Sam 'backers in this example) read their run/pass keys (inside triangle: guard-center-guard) and sink to a depth of 10-12 yards outside of the hash marks.

These linebackers must get depth to cushion the inside seam and dig while driving downhill on the shallow crossing routes and checkdown.

I mentioned the strong safety above as a run defender in Cover 3. Here, versus a Pro "I" formation, the strong safety reads the tight end for his run/pass key and must contain the run game by squeezing the edge with a "hammer" technique (attack lead block with inside shoulder).

This allows the safety to force the play back inside to the defensive pursuit.

Cover 3 vs. Slot Formation

In a zone defense, the cornerbacks don't "travel" versus a slot formation to match to their coverage like we would see in Cover 1 (man-free).

Instead, they become primary run support players to the back side of a slot formation (closed side) with the strong safety rolling down over the No. 2 receiver (slot receiver) to the open side.

Using an example of the Steelers' Cover 3 shell out of their 3-4 front, let's take a look at how the defense aligned versus the Patriots' "Unit Slot" formation with Ace/12 personnel on the field.

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As you can see, the cornerback walks down to the closed side of the formation (two tight ends in a wing set) and becomes the primary run support defender (contain/force).

Once the cornerback clears his run/pass keys (tight end), he will sink with a "bail" technique to the outside third. This is where NFL offenses often attack the cornerback with vertical releases from the two-tight-end wing alignment.

To the open side of the formation (slot alignment), the strong safety (Troy Polamalu) rolls down over No. 2.

Polamalu must reroute any vertical release from No. 2 before working to his curl-flat drop to take some stress off the open-side cornerback and free safety on a possible inside seam route.

The open-side cornerback is playing off and will flat-foot read through the three-step game before getting into his pedal to maintain the cushion versus the receiver in the outside third.

The free safety (Ryan Clark) plays the deep middle of the field as he would versus a balanced Pro formation. However, because of the slot alignment, Clark needs to split the formation in his drop to get over the top of the outside 9 route.

Seahawks' Cover 3 Technique and Alignment

The Seahawks maximize their personnel in Cover 3 by aligning the cornerbacks in press looks outside of the numbers to pattern match any vertical release/stem.

Think of cornerbacks Richard Sherman and Byron Maxwell playing press-man technique at the line of scrimmage with the protection of free safety Earl Thomas in the deep middle of the field.

This is the Seahawks' nickel Cover 3 alignment versus the 49ers' Doubles Slot formation (3x1) with Posse/11 personnel on the field (3WR-1TE-1RB).

Credit: NFL Game Rewind

The underneath zone defenders (curl-flat/middle hook) play the same landmark drops/techniques as we talked about above in the base Cover 3 examples.

However, look at Sherman and Maxwell. Both cornerbacks are aligned in press (with an outside shade). This allows the Seattle corners to jam the No. 1 wide receivers and run with any vertical stem down the field (pattern match).

If the cornerbacks see a smash route (think smash-7 combo), they can drop No. 1 and sink to the outside third (standard Cover 3 drop) to play a possible corner route from No. 2.

Now, let’s see this play out using the All-22 tape from the Rams-Seahawks matchup this past season in Seattle.

Credit: NFL Game Rewind

With the Rams using max-protection (two-man route scheme), both Maxwell and Sherman match the vertical release of the receivers (from an outside leverage position) to funnel both the post and dig to Thomas in the deep middle of the field.

Underneath, the four zone defenders gain depth and get their eyes back to the quarterback. This puts them in a position to drive downhill aggressively on the checkdown or tight end in the flat.

Given the top-tier ability/range of Thomas in the middle of the field, plus the press skills of Sherman and Maxwell, Seattle can use this style of technique in its Cover 3 defense.

But we can't expect the rest of the league to follow until they can match the overall talent in Pete Carroll's secondary.

The Safety's Role in 3 "Buzz"

Cover 3 "Buzz" allows the defense to disguise their three-deep zone by dropping the strong safety down inside of the numbers as a middle-hook defender.

This allows the strong safety to play almost as an inside "robber" with the linebacker bumping out to the curl-flat and assuming the primary contain/force responsibilities versus the run game.

Defenses will show a two-deep shell or quarters look in their pre-snap alignment and drop the safety with his depth based on the down and distance situation.

In 3rd and 2-6, look for the safety to tighten his alignment. And in longer down-and-distance situations (3rd and 7-10, 3rd and 11-plus) the safety will sit deeper (near the sticks) to cushion the seam route while being in a position to drive on the checkdown.

Here's an example from the Seahawks' Super Bowl win over the Broncos with strong safety Kam Chancellor dropping down from a two-high look.

Credit: NFL Game Rewind

Just as we talked about above, the Seahawks press their corners on the outside with Thomas dropping to the deep middle of the field.

And with the Sam 'backer bumping out over slot receiver Wes Welker, Chancellor can drop down to the closed-side middle hook.

Credit: NFL Game Rewind

This is a basic curl-flat combo from the Broncos with tight end Julius Thomas removed from the core of the formation as the No. 1 receiver to the closed side. The Seahawks cornerbacks squeeze/funnel the curl routes and force Manning to target Welker on the underneath checkdown.

And because of Chancellor's pre-snap depth, the strong safety is an ideal position to drive downhill on Welker to deliver a clean, violent hit on contact.

In Cover 3 "Buzz," the defense can drop either the strong or free safety (Seattle will use Thomas as the middle hook defender also) while showing the quarterback a different look at the line of scrimmage.

It's a smart (and easy) way to disguise three-deep coverage while creating a "robber" look inside of the numbers.

Cover 3 "Cloud"

Cover 3 "Cloud" is a situational coverage for defenses that want to play three-deep in the secondary while using Cover 2 technique at the line of scrimmage to jam/reroute a top-tier wide receiver with help over the top.

Take a look at the diagram of Cover 3 "Cloud" I drew up versus Posse/11 personnel in a 2x2 Doubles formation.

Matt Bowen/Bleacher Report

With a two-high safety alignment (and corners in a press position), the defense will roll the coverage at the snap to create a three-deep look.

To the closed side, the strong safety (SS) rolls to the deep outside third with the free safety (FS) moving to the deep middle of the field. To the open side, the cornerback (RC) drops to the outside third using a "bail" technique.

Underneath, the closed-side cornerback (LC) jams the No. 1 receiver (Z) to force an inside release and then sinks to cushion a possible 7 (corner) route (think Cover 2 technique).

The idea is to impact the release of No. 1 with the strong safety over the top in a deep third drop (also called a "cloud" coverage).

The two inside linebackers (M, S) drop to the middle hook landmarks with the nickel (N) playing the curl-flat technique to the open side of the formation.

Cover 3 "cloud" can be used in specific game situations versus a wide receiver with deep-ball ability to disrupt the release and take away the 9 route down the sideline.

Seven-year NFL veteran Matt Bowen is an NFL National Lead Writer for Bleacher Report.

Follow @MattBowen41