How to identify if a run play is Inside Zone or Duo

5 things that players look for immediately when the NFL schedule is released
May 7, 2020

The rise of social media film watchers and All-22 tape being available via NFL Game Pass has led to countless discussions about football schemes. One discussion that has dominated for years now is a debate on whether a specific run play is “Inside Zone or Duo.”

“Is this Inside Zone or Duo?” is a familiar phrase for film watchers on social media, whether it’s a serious or sarcastic question. They are two run plays that are quite different but have the appearance of looking similar on film.

Inside Zone is a zone run scheme, where the offensive linemen all step in the direction of the run play, with double teams that are vertical and horizontal. The running back is on an angle chasing the butt of the center, which might be described differently depending on the offense.. An inside zone can be run to a tight end or not, and it’s most often successful when the running back finds his way to the backside A gap.

Duo is a gap scheme run and is often called “power without a puller.” It’s a downhill run with offensive linemen moving vertical up the field, attempting to build in as many double teams as possible. The running back is downhill in the frontside A gap. Duo is run exclusively to the tight end so you can start building your double teams with him. The running back finds most success running this play to the call side, but he can hit backside for success if it presents itself.

As you can see, these plays can look the same drawn up, but they aren’t the same on film. So I’ve created a handy flowchart to help you with identifying “Inside Zone or Duo”:

There are two things worth noting here. First off, there is one inside zone that is a specific formation vs. a coverage look where the center can work backside. It’s rare and almost out of the game by now. Secondly, if you notice, the running back’s path isn’t mentioned on the flowchart. That is by design. While a running back’s path is often used to determine if the run is an Inside Zone or Duo, it should be the last factor. On Inside Zone, the back takes an angle toward the playside, and he’s reading the frontside defensive tackle through to the linebacker. On Duo, the running back is straight downhill, reading the middle linebacker

If that chart is all you need, you can stop here. Below, I’ve put together an explanation for everything on the flowchart.

1. Run to the TE (Y)

Duo is a play run exclusively to the tight end, or the Y. You can immediately eliminate the run from being Duo if the running back is moving away from the tight end.

If the running back is moving in the direction of the tight end at the snap, you have the first step of Duo.

2. Does the Center work to the frontside?

The frontside of the play is toward the tight end. If you’re running right, does the center go right at the snap? If you’re running left, does he work to the left? Another way to put it is if the center is working to the Mike linebacker. This is the best step for identifying Inside Zone or Duo.

The center working toward the tight end to the Mike linebacker. This is Inside Zone.

The center is working away from the tight end, to the Will linebacker. So “NO,” he’s not working frontside. This is Duo.

3. Backside OT blocks the DE (Big on Big)

If the center’s direction is giving you a tough time, you can check on the backside OT. For Inside Zone, the backside offensive tackle is taking zone footwork to the called side of the run. The backside defensive end is being blocked by a tight end, or a ghost tight end.

In this case, the backside offensive tackle is working to the playside. This would be a “NO,” making it Inside Zone.

In Duo, the backside offensive tackle is blocking big on big because the frontside double teams are able to handle the linebackers in the box. Also, to get super nerdy here, because of the running back’s downhill path, the offensive tackle can’t step inside. If he allows the defensive end to run down the line of scrimmage, he will easily tackle the RB for a loss. On a zone play, the back is started out at an angle away from the defensive end, taking him longer to run down the play if he’s not blocked.

If you’ve stayed this long, then you’re waiting for see these plays in full.

Inside Zone. Run to the tight end, the center is working frontside and the backside OT is not blocking the defensive end. Lastly, the running back is taking off at an angle.

Now we end with Duo. The run to the tight end, but the center is working back. The backside offensive tackle is working to the defensive end and the running back is going downhill, even if it’s off a jab footwork.

When I first started to write, my goal was educating the masses on offensive line play. Feels like I hit my goal here. Hope this was easy to consume and you use this flowchart in the future.