Duo is a great running play.
It’s versatile, so it can be run effectively out of different personnel packages and formations, and it works against a variety of fronts. It can also be used for different purposes from the offense’s perspective. Want to knock the defense off the ball and play a more physical brand of football? Call Duo. Want to provide a change of pace from your zone-running schemes? Call Duo. Want an answer for aggressive linebackers and blitzes inside? Better call Duo.
So what is Duo? It’s a gap-scheme run (down blocks to the play-side) without pullers like you have on power and counter. It generally gets multiple double-teams, although the number of doubles will vary based on the formation and defensive front.
Below, you can see how the 49ers ran it with success against the Steelers during Week 1 of the 2023 season:
I won’t go through the count rules, but the basic premise is that each blocker is responsible for a defender, but if a blocker’s backside gap is clear and their assigned man is off the line of scrimmage, they double-team until their man attacks or declares.
Below you can see the double-teams and individual assignments from the play above:
As a slight wrinkle, the 49ers used motion right before the snap to get their second tight end across the formation to block the defender they identified as the Sam linebacker.
Now notice the two double-teams, the calling card of Duo:
In general, a wide receiver is responsible for any safety coming down in the box, which you can see the 49ers accounted for here:
The running back’s initial read is the middle linebacker. Below, you can see Christian McCaffrey take the hand off and get his eyes immediately on the Mike:
He read that the Mike was staying to the outside of the double-team (he also likely felt multiple black jerseys to his right), so he went inside:
When McCaffrey saw the Will linebacker moving inside and the crease in the opposite A-gap created by the double-team, he quickly accelerated through it:
Center Jake Brendel would do a great job of pinning the nose tackle inside after the Will linebacker declared, helping to create that alley for McCaffrey. The result was a 17-yard gain:
This next example comes from the Cowboys during the 2021 season. The offense was also in 12 personnel, but they aligned in a tight bunch. Below, you can once again see the assignments and double-teams: