Slant-Bubble RPO vs. Multiple Defensive Structures

How the Kansas City Chiefs used the Slant-Bubble RPO to fix their numbers problems against the Pittsburgh Steelers on Christmas Day.

By my count, the Kansas City Chiefs ran 18 RPOs out of their 63 total plays in their Christmas game against the Pittsburgh Steelers (that’s 29% of all plays, so it’s an even higher percentage on called runs). I don’t watch enough of the Chiefs to know if these are normal numbers, but it caught my attention in the few drives I watched live.

With defenses playing with “light boxes” that allow them to present a favorable run box to the offense while being on the edge forcing the give and ready to fit, RPOs have seemingly gotten harder to run.

Yet the Chiefs, one of the league’s most successful teams, made RPOs a central part of their game plan against the Steelers. This raised an intriguing question: how are they making it work?

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Against MOFO Zone

The first time the Chiefs ran this Slant-Bubble RPO was against MOFO Zone where they read the backside inside linebacker off a zone run scheme. They were in 11 personnel, but only blocked the scheme with their 5 offensive linemen, allowing their tight end to be the bubble runner. Take a look:

The Steelers’ defense is in a Middle of the Field Open structure with the nickel to the field (the same way the run is toward). That makes the Will the read. If he doesn’t fit, then the quarterback should hand the ball off. If he does fit, there should be room to throw the slant. On this play, he doesn’t fit and the quarterback hands the ball off. The nickel to the frontside also didn’t fit. That left five defenders in the immediate run fit (or the run box) for the five offensive linemen to block.

The read is that straightforward when the defense is in a MOFO structure because there is one less underneath defender. Therefore, the defender who is in the fit is also likely to be the flat defender unless the defense is playing Cover 2 whereas there would be 5 underneath defenders. At that point, the handoff would likely still be successful because the numbers would be the same as the example here (Quarters).

Here’s the read player circled as both the run fit read and the Slant-Bubble read:

However, the Slant-Bubble concept is not great against a MOFO structure because the safety is can sit on that slant. So while the slant “comes open” post snap, it’s not a safe bet, and Mahomes’ give (which looks to be predetermined by the one-handed nature of it) is the right play since the numbers in the run game are in the offense’s favor.

In contrast, a MOFC structure is ideal for the Slant-Bubble concept.

Against MOFC Man

The second time the Chiefs ran a Slant-Bubble RPO, they did so out of an 11 personnel 3x1 set off zone action. By adding the tight end into the blocking scheme, the offense can now block six defenders leaving any seventh fitter as an unblocked threat.

The mechanics of the read are the same for the quarterback. Once again, identifying the structure of the defense helps the quarterback make the read before the snap. Last time, the structure was Middle of the Field Open, but here it’s Middle of the Field Closed. Since one safety is in the middle of the field, that means the other safety has to be somewhere near the box. In this case, the down safety is over the number two receiver.

The quarterback then knows he’s dealing with a numbers problem he’ll need to fix by throwing the pass option of the RPO. That concept, however, has a read in and of itself that I’ll touch on later.

Here’s the full play — pay special attention to the quickness of Mahomes’ decision and his mesh (or lack thereof):

In addition to there being one safety in the middle of the field, the tight end’s motion gives clues to what’s going on. A man travels with the tight end thus signaling to the quarterback that the defense is in a Closed Man structure.

The trick with defenses is that the numbers in, near, or out of the box don’t always tell the full story for how many defenders are allocated to the run fit. Man coverage makes it real easy to see who is in the fit because each defender responsible for one of the five eligibles is first responsible for that man as opposed to fitting the run. So that means if seven defenders are in the box, then the four defenders outside the box, save the middle of the field safety, are not fitting the run immediately.

Thus the man indication solidifies that the offense has a numbers problem in the run game. Therefore, the ball must be thrown — hence the quick mesh from Mahomes.

In addition to having a concept to alleviate the run problem, the Slant-Bubble concept attacks this specific structure by putting the flat defender in a bind. In man coverage, there is no “flat defender” but rather a man covering the number two receiver. As a result, the quarterback can confidently throw the slant because the defender in the slant window will be pulled out of the slant window by the bubble.

Against MOFC Zone, that window is not so sure a bet.

Against MOFC Zone

The third time the Chiefs went to this play, they gave Mahomes a motion like the one prior to give him clues. And once again, the structure is a clue too.

The motion serves two purposes as far as I can tell — first, to identify man or zone and second and more importantly, to force outside leverage from the cornerback on the slant route. Since the motion brings the tight end from the number one position to the number two, the new number one position is already close to the formation.

Usually, defenses will play with divider rules in a closed structure. Since the new number one receiver is inside the numbers, the defense will most likely play with outside leverage since the closed/post safety is available to help inside.

In contrast, a wide split from the number one receiver would dictate inside leverage since the closed/post safety would be too far away to help. In essence, the divider rules allow the defense to maintain leverage given the space the wide receivers’ alignments present the defense to cover.

Since the Chiefs are in a 2x2 formation without the tight end attached, the quarterback needs to find the 6th defender since their are only five blockers (the five offensive linemen). In this case, that’s the weak side, inside linebacker:

The Slant-Bubble RPO is interesting because it’s a route concept that where you’re reading a player who is not the usual read on the concept. So as the quarterback, it’s almost as if you need to be sure the flat player (the normal read on Slant-Bubble) won’t be an issue. Perhaps that is why the Chiefs pair this RPO with motion so often).

Therefore, the risk is if the sixth man fits but the flat player doesn’t widen to take the bubble. Not the case here:

The Steelers happen to blitz the sixth man, so the run fit read is simple. Additionally, the flat player is aligned over the number one receiver pre-snap and immediately widens post-snap though his eyes are inside. Mahomes’ ball handling is once again decisive and hardly a mesh. That signals he must have known he would have a good chance at ripping the slant.

Against MOFC Man

This fourth call is the exact same as the one prior, though now against Closed Man. The defensive backs switch man responsibilities after the motion and play with inside eyes, but they track each receiver as if in man.

Notice Mahomes’ ball handling and mesh — it’s much more read-like than the other give in the first example:

The read hasn’t changed though. If the weak side inside linebacker (the sixth fitter) fits, then throw. If he doesn’t, then give. At the decision point in the mesh, the read player is sitting in the slant window so Mahomes hands the ball off:

Conclusion

The Chiefs’ Slant-Bubble RPO is a good example of the use case for RPOs — fix the numbers problem when necessary and take advantage of open space. And while this RPO is a post-snap read, the pre-snap identification of the structure can help the quarterback know before the snap what type of read he’s dealing with and if he’s in a numbers problem from the get-go.