Jaguars film room: Inside Zone vs Duo

Zone or Duo?! memes have become popular over the last few years for NFL film enthusiasts. With the Jacksonville Jaguars running both concepts this preseason, Big Cat Country is here to help uncover the differences (and similarities) between the two plays.

The confusion comes from how similar the plays look. These similarities include the downhill nature of each concept, how they mostly run from single-back formations, take place between the tackles, and how the runner occasionally cuts back against the grain. These all play a factor in the difficulty of determining the play call. Identifying each play is knowing the subtle differences between technique and the read keys.

A good starting point is observing the double teams. While both run schemes can have double teams depending on the defensive front, there are some tells that give away the play. If the OL is working around a defensive tackle to get up to the second-level defender, it’s most likely inside zone. If the offensive line is working through the defensive tackle up to a linebacker, it’s most likely duo.

Working “around” a DT just means the offensive player is responsible for the second-level defender the entire play, but his path to get there might involve helping a teammate with a chip, or a one-handed shove.

Working “through” the DT means the double team is more aggressive, meant to push the DT upfield, while the offensive lineman’s eyes are on the linebacker at the second level. The direction the linebacker flows dictates which offensive player is responsible. The lineman to that side will come off the double team and engage the linebacker.

In addition, an offensive lineman’s first few steps after the ball is snapped can be very telling. The more lateral these initial steps are, the more likely inside zone has been called. Conversely, if each lineman’s first few steps are aggressively upfield, most likely you’re witnessing duo.

Unfortunately, it’s often not as cut and dry as the above clips may suggest. That’s where the difficulty lies. Understanding the design of each concept can often help in determining which one was called in the huddle.

Inside Zone

Inside Zone is a concept designed to run between the tackles. Broken down into its simplest form, each offensive player is stepping play side and responsible for any defender who enters their zone. As is often the case in football, nothing is as simple. Many factors come into play, and communication is key for offensive linemen in order to get everyone blocked.

One method to ensure every defender towards the play side is accounted for is leaving the backside end man on the line of scrimmage (EMOL) unblocked. This forces the defender, who is often the contain player, to make a decision. If he comes crashing down to make the play, offenses will tag the play call allowing the quarterback to keep the ball and get around the edge. If the EMOL comes upfield too far, he opens up a cut-back lane for the running back.

By leaving the EMOL alone, offenses gain a numbers advantage to the play side. This allows the running back to square his shoulders to the line of scrimmage and react to the flow of the defense. While the back’s aiming point is often between the offensive tackle and guard, the play can hit anywhere on the line of scrimmage. Offensive linemen are taught that every block could be the point of attack, therefore, equally important.

The running back will read the first defensive lineman outside of the center on the side of the play call. It’s precisely this read that you’ll often see the defensive tackle engaged with only one offensive lineman and avoid a double team. This allows the defensive player to declare a side, making it easier for the running back to determine where to cut. Inside zone is a one-cut-and-go type run play, so double-teaming the DT would often lead to indecision from the running back, slowing the play down.

Offenses lean heavily on inside zone because there are many variations that can be installed. These involve changing one player's assignment while keeping it the same for everyone else. A coordinator just needs to tag the player at the end of the play call which should ensure everyone defensive player is accounted for.

Duo

Duo is a strong side gap scheme run play. It’s often referred to by coaches as an attitude play; a tone-setter. Offensive linemen are tasked with aggressively pushing first-level defenders (defensive line) upfield into second-level defenders (linebackers). How they go about doing this is with as many double teams as the offensive formation and defensive front allow.

Since the double teams are taking place at the first level, it’s impossible for the running back to read a defensive tackle. So for duo, a back gets his eyes on the second level and is reading the play side middle linebacker. Whichever direction the defender declares, the running back cuts opposite. This is why you often see a cutback with duo because the flow of the play usually gets the linebacker to overcommit to the play side. The running back will then stick his foot in the ground and cut against the grain while getting vertical.

One variation of Duo that helps the timing is having the running back to a jab step at the snap. This allows the double teams to develop while also allowing the linebacker to commit to a side before the running back receives the hand-off. A subtle adjustment that gives the ball carrier an easier read.

The Jaguars' versatility at the running back position allows Pederson to call both inside zone and duo with confidence. Both plays also empower offensive linemen to be aggressive without fear of making a mistake. Travis Etienne and Tank Bigsby are skilled enough to make the linemen correct, whatever decision they make on the blocking schemes.