In a disappointing 23-14 loss to the Arizona Cardinals, the San Francisco 49ers’ offense showed something that we had never seen under Jim Harbaugh: five wide receivers on the field at once.

According to Pro Football Focus, the 49ers sent five receivers on to the field for 14 snaps against the Cardinals with an additional 14 snaps having at least four wide outs on the field. San Francisco spent the majority of two possessions operating out of an empty backfield formation with those five receivers spread across the field in a look that seemed to go against everything we’ve come to know about Harbaugh’s offense.

With tight ends Vernon Davis and Vance McDonald unavailable for the game, using all those receivers was partially out of necessity. Third-stringer Derek Carrier has shown some flashes in limited action so far this season, but it would be hard to argue that he should be getting snaps over the likes of Stevie Johnson or Bruce Ellington. But what started as necessity might have turned into the beginning of a trend we’re likely to see continue throughout the rest of the season.

Combined with the no-huddle — though not really up-tempo — the 49ers had a lot of success operating out of this five-wide, empty-backfield set. Let’s roll the film and take a closer look at the newest package in the 49ers’ offense.

Smash

It’s no surprise that the 49ers favorite passing concept would find its way into their latest offensive wrinkle. As Harbaugh and Roman love to do, San Francisco’s top passing options (Michael Crabtree, Anquan Boldin, Stevie Johnson) are all aligned to the inside of the formation in an attempt to get them matched up on Arizona’s weaker pass defenders.

On this play the Cardinals choose to rush five and play Cover 1 behind them, giving them man coverage across the board with a single safety deep in the middle of the field. This would typically be a situation in which Colin Kaepernick would choose a side of the field to work the smash combination based on his preferred match-up on the corner routes. Instead, he looks to the middle of the field to Johnson.

Johnson is matched up on rookie safety Deone Bucannon, a mismatch heavily favoring the 49ers. Man coverage on the inside is not Bucannon’s strong suit and so far this season the Cardinals have mostly used him as a de facto linebacker in their sub-packages. Asking him to cover a shifty route runner like Johnson in space is rarely going to end well. Johnson runs what’s commonly referred to as a "jerk" route. The jerk route is basically a shallow crossing route in which the receiver fakes as if he’s going to settle in the middle — causing the defender to hesitate — before continuing across the field.

The results are predictable. Johnson gets quick separation over the middle and gives Kaepernick an easy completion. Better ball placement potentially gives Johnson an opportunity to do more after the catch, but he moves the chains and converts the third down nonetheless.

Stick-Levels

A couple of plays later, Kaepernick was again presented with a mismatch on one of his slot receivers. From the Cardinals’ pre-snap alignment, Kaepernick has a good indication that Arizona is going to be in zone coverage. The secondary — sans Patrick Peterson at the bottom of the image — is in off coverage with their eyes in the backfield and neither Michael Crabtree nor Johnson has a defender directly over them.

Rather than the mirrored concept (same routes to each side of the field) we saw in the first play, Roman has packaged two different passing concepts on the same play giving Kaepernick a three-step route combination (stick) to one side of the field and a five-step combo (levels) to the other. From there, it’s on Kaepernick to choose which side of the field he’s going to work based on his read of the defense.

It’s an easy choice as Kaepernick sees veteran linebacker Larry Foote as the nearest defender to his best receiver, Crabtree. Remember all that stuff I said about Bucannon in pass coverage? Now imagine a much slower, 34-year-old linebacker version of that and you basically have Foote.

Kaepernick has another easy completion, giving the 49ers another easy first down. The spread formation, the alignment of personnel, and the no-huddle all contribute to getting the Cardinals in a vanilla coverage with an aging, run-stuffing linebacker matched up on the 49ers' best pass target.

Hi-Lo

Following that initial drive, the 49ers would possess the ball just two more times in the first half, neither of which saw the no-huddle, empty-backfield look that dominated the opening possession. After a couple of quick drives to start the second half, San Francisco would go back to it late in the third quarter, looking to jump start their offense.

The 49ers have a hi-lo concept in the middle of the field, something they also ran on the first drive of the game and came back to here. Johnson and Anquan Boldin are both running hitch routes (low) — with the option to work outside towards the sideline depending on the coverage — with Crabtree on the dig route behind them (high).

After finding Johnson on the underneath route earlier in the game, Kaepernick opts to throw over — or between in this case I suppose — the second level of the defense to Crabtree. Johnson’s hitch is able to hold the linebackers just enough — Foote actually looks to jump Johnson’s route rather than Crabtree’s once Kaepernick begins to throw — to create space for Crabtree’s dig route.

It’s a fantastic anticipation throw by Kaepernick, something he still needs to do more consistently. As you can see in the shot above, Kaepernick has started his throwing motion before Crabtree has cleared the first linebacker and gotten into the passing window in the middle of the field.

The 49ers’ passing offense has primarily focused on the sidelines when throwing the ball down the field. But with the increased space in the middle as a result of the spread formations, Kaepernick attacked the middle more frequently against Arizona than any other game I can remember.

Slant-Flat

While the 49ers were predominantly able to get the Cardinals in more simplistic defenses when going with their empty package, Arizona has the blitz call on here. With both linebackers up at the line of scrimmage in the A-gaps, the Cardinals’ secondary is left in man coverage without safety help, or Cover 0. And the 49ers are in a great call to beat it.

To the wide side of the field, San Francisco has one of the most common quick-passing game concepts dialed up: slant-flat. The two outermost receivers, Brandon Lloyd and Crabtree, both run slant routes with the inside receiver, Johnson, running directly to the flat.

This combination creates a natural rub on the defenders and frees up the flat route to the outside. Even though Arizona has an unblocked rusher off the edge, Kaepernick is able to get the ball out quickly to a wide open Stevie Johnson. With no third-level defenders, Johnson has loads of green grass in front him and picks up 32 yards before being forced out of bounds.

★★★

With all of the success San Francisco had in this package, many have posited the question, why not keep going back to it? The run it ’til they stop it approach sounds good in theory, but is rarely a good idea. Put simply, NFL defenses are really good. If you continue to show them the same looks over and over, eventually they’re going to find a way to stop it. At least part of the reason the 49ers were so successful in this package was because it was only part of the gameplan.

One thing seems certain, we’re likely to see more of this empty, no-huddle package from San Francisco’s offense going forward. Kaepernick looked incredibly comfortable operating with his receivers spread across the field and consistently made good decisions on where to go with the football. The 49ers’ offense is evolving and this is just the beginning.