Basic Defensive Coverages Series: Cover 4


We’re continuing our look at basic defensive coverage schemes and how the Buffalo Bills have used them. These are 101-level introductions that just begin to hint at the schematic complexity NFL defenses employ against the best offenses in the league, but they’ll give you a leg up in trying to understand why a defensive back was in a particular part of the field or why that linebacker ended up covering a wide receiver.

Our fourth coverage scheme is Cover 4. We’ll break it down below, but let’s start with how the Bills utilize it.

Bills’ Usage

According to Sports Info Solutions, the Bills used Cover 4 against 121 pass attempts, which ranked seventh in number of attempts. The Bills’ defensive statistics (and ranks) when using Cover 4 against pass attempts are pictured below. This number from SIS may differ from what you might find elsewhere because it’s based on whether or not there was a pass attempt. For instance, if the offense used a running play while Buffalo had set up in Cover 4, it would not show up here.

Compared to the league, the Bills were exceptional in their use of Cover 4. They were top 10 in Total Points Saved, TPS/Play, EPA, and EPA/Play. Being that high in both cumulative and rate statistics means you’re killing every which way.

Stat (Rank)

Bills’ Most Important Players (not named Josh Allen) Entering 2023: #1 Spencer Brown

Cover 4 Zones

After reading through the previous articles you should be able to guess a little about the structure of Cover 4. Cover 4 is remarkably versatile and has numerous versions. We talked very briefly about pattern matching in the Cover 3 piece, and pattern match Cover 4 has so many variables it would be too much to truly investigate here (maybe an idea for next offseason, hmm).

If you thought communication in the back seven mattered in Cover 3, it is an absolute imperative in Cover 4. Receivers have to be passed off both effectively and fast, routes have to be diagnosed accurately on the fly, and like all zone schemes, once the pass is completed players must rally quickly to the tackle.

For the sake of time, we are using diagrams from Breakdown Sports.


The yellow circles make the name obvious: the deep portion of the field is divided up into four sections with the outside CBs and Safeties each taking a section.

Like all the previous coverages, the design starts with the safeties. It will be important to remember that receivers are assigned numbers beginning from the outside of the field on both sides and moving in.

Safeties: We have intentionally kept defending the run at the outskirt of our conversations here because I really wanted to focus just on the coverage aspects to avoid each article becoming a book (and because I’m still learning run fits). But we have to start here with reading the run for the safeties because they have to be prepared to come up from a position that starts 9-12 yards deep. The Safeties’ reads start with reading the QB for run/pass and move to No. 2. If it’s a pass and No. 2 goes vertical, either S must respect his Cover 4 zone. If No. 2 stays shallow, then the Safeties can shift their read to the No. 1 on their side and bracket.

Cornerbacks: The outside CBs can start in either press or off position, and their read begins with the No.1 receiver on their side. They want to maintain outside leverage on No. 1. The CB also must read and react to how the S on his side plays the run. If there is a play-action fake, and the S bites too hard, the CB has to adapt his coverage responsibilities, paying attention to the potential of the No. 2 going deep, where the S should have had him. The CB is now essentially playing a deep half.

Communication on corner and post routes is critical in Cover 4. If the No. 1 runs a 10-yard post, he will be picked up by the CB on his side and then must be transferred to the S, and vice versa for a corner route from No. 2. This route combination is called an 87 because of the way the route tree is numbered. You can see an example on the left half of the second diagram.

Weakside LB and Nickel CB: (The diagram shows three LBs, but since the Bills primarily run nickel coverage, the S here will be for the nickel CB). The Will and the NCB will start their reads with the Guards for pass/run. On a pass read, they are working from the inside hook area out to the flat. They also need to try to create a collision with underneath crossing routes or a deep route from No. 2. While the collision doesn’t really offer coverage, it disrupts the timing and location of the route.

Mike LB: The Mike is reading the QB through the IOL for run/pass, and on a pass read is responsible for the hook area and to interfere with any crossing routes.

Defensive Line: Once again, a four-man rush from the DL.

Man Only Deep (MOD)

MOD is a version of Cover 4 where the deep zones turn into man coverage.

The underneath responsibilities remain the same as Quarters, but the defensive backfield plays out differently.

Safeties: The S reads No. 2 to No. 1. If No. 2 goes vertical, the S has him man-to-man, regardless of if the route takes him into one of the other Cover 4 drop zones. If No. 2 stays shallow, the Will or NCB picks him up, and the CB doubles No. 1.

Cornerbacks: If No. 1 goes vertical, the CB rides him in man. If No. 1 is shallow, then the CB will stay deep in case of a vertical route from No. 2.


In Palms, the underneath remains the same as Quarters.

Safeties: The Safeties are still reading No. 2 to No. 1, but their response has changed. If No. 2 goes vertical, he takes his deep 1/4th, similar to quarters. If No. 2 has a shallow route, the S now plays a deep half, like Cover 2, including covering No. 1 deep.

Cornerbacks: The outside CBs are now also reading No. 2. If No. 2 goes vertical, the CB plays his deep 1/4th

The example below shows No. 1 on the left going deep, picked up by the S, and No. 2 on the right with a corner route picked up by the outside CB.

Bills’ Most Important Players (not named Josh Allen) Entering 2023: #2 Stefon Diggs


This brief introduction to Cover 4 doesn’t even begin to address all the options for this scheme. Thumbs, Switch, C4 Robber, etc. are all variations we didn’t get to. Cover 4 is a remarkably malleable system, and I hope you can start to see some of the ways in which the Bills utilize it as one of the top Cover 4 teams in the league.

Next week, we close the series with Cover 6.

You can find Chris on Twitter (@lowbuffa), getting dirty in #MafiaGardens, or watching football. Go Bills!