Even with top targets like WR Michael Crabtree and TE Vernon Davis out for San Francisco, this kind of showing for the Colts defense was completely unexpected. The 49ers dominated Green Bay in Week 1, and the Seattle defense that kept them at bay in Week 2 is much more talented (at least on paper) than the Colts' unit.
Despite any pregame notions, however, the Colts went into San Francisco and held the 49ers to just one scoring drive. After San Francisco went on a seemingly easy nine-play, 91-yard drive, they struggled to even get into Indianapolis territory for the rest of the game, not getting past the Colts' 40-yard line until the final drive (when they were already down 27-7).
So how did Chuck Pagano manage to stop what was once a high-flying offense? That's what we'll look at in this week's film breakdown.
Key No. 1: Make San Francisco Pass the Ball
The 49ers have been bashed for "losing their identity" and "abandoning the run" this week, and while this isn't meant to completely exonerate Jim Harbaugh from that, it would be remiss to not mention that the Colts defense had a hand in forcing the pass.
Yes, the 49ers' first half rushing numbers look good, rushing for 102 yards on 16 carries. However, those were heavily skewed by the 49ers' first two drives. After those two, the Colts did a phenomenal job of keeping the 49ers at bay.
Yes, the 49ers dominated the Colts' front seven on those first two drives, but after that they were decidedly better.
To contrast, let's look at a play from San Francisco's touchdown drive compared to a later run.
Pre-snap, the Colts safeties shift, as Delano Howell comes forward into the box and Antoine Bethea drops back into a single-high safety look. Against eight men, you wouldn't think that San Francisco would have much success running the ball, but here the 49ers run to the opposite side, completely nullifying the Colts' extra man.
What you'll see on the San Francisco side is the tight end dipping inside, blocking Ricky Jean Francois one-on-one and the left tackle pulling outside to block Erik Walden.
Right off the bat, you see a big problem. Erik Walden has driven his man upfield, leaving a gaping hole between the right tackle and right guard. The beauty of blocking Walden and Jean Francois with only one man is that it allows the right guard to get out into the second level, as he goes on to block Kelvin Sheppard out of the play.
Now that Gore is through the hole and looking for big yards, we watch the fullback. At first it seemed as if he would be blocking Jerrell Freeman, coming from the other side. However, Freeman couldn't sift his way through the traffic quickly enough, and the San Francisco fullback smartly runs right past him with eyes on Greg Toler. By taking Toler out, Gore is able to gain about 6-10 extra yards before Antoine Bethea is able to come up and make the tackle.
Meanwhile, Sheppard (blue), is completely unable to shed the blocker and make a play on Gore, who never gives Sheppard a second thought as he sprints right past him.
In contrast, look at these two plays from later in the game.
In this first one, Robert Mathis holds his ground on the left side, not giving Gore anywhere to bounce outside if the middle was clogged. As it turns out, the middle was clogged, because unlike Jean Francois, Walden or Sheppard in the first play, Josh Chapman was able to shed his block and stuff Gore for no gain.
In the second play, we see a very similar play from San Francisco, but to the other side. Erik Walden is the point of attack again, but this time, instead of shooting up the field, he holds back. This causes more activity right in the running lane, causing the FB to help block Walden (leaving Vontae Davis free to come up and support on the play) and allowing the other Colt defenders time to get to Gore.
While the play gained seven yards, and was one of the more successful runs of the second half for San Francisco, it's easy to see how Walden's actions can hurt/help the defense so drastically. This run only went for seven rather than 22 yards.
Key No. 2: Smothering Coverage on Wide Receivers
This one should be obvious: Colin Kaepernick struggled all day, and it was plainly evident that he was having a difficult time finding open receivers.
The numbers reflect this: San Francisco receivers caught just seven catches for 79 yards. Vontae Davis, Greg Toler and Darius Butler all played extremely well in coverage, and it's something that any analyst that has watched the game noticed.
But don't take my, or Daniel Jeremiah's, word for it. Let's take to the film to see it for ourselves. Without the All-22 film (doesn't come out until Wednesday nights unfortunately), we can't assess every play, but we can get good angles on a few plays.
Vontae Davis is matched up with Anquan Boldin in the slot on the left side on this play, a rarity for a corner who lines up split wide right during the vast majority of plays. Greg Toler is responsible for Kyle Williams on the far left side. Both corners are in man-to-man on this play.
Kaepernick tries to get the ball to Boldin, but has to throw the ball too far ahead of him due to Davis' tight coverage. Any closer to the receiver and the throw is likely batted or even picked off. In the background (blue) you can see Toler is right on Williams as well.
But of course, the cornerbacks weren't the only ones to shut down the San Francisco receivers. Both safeties did a notable job as well, exemplified by a pair of hits and passes defensed by Delano Howell.
Here, Howell forces a punt with a hit/ball swipe on rookie WR Quinton Patton, knocking the ball from Patton's grasp.
This was Howell's Mona Lisa, his cherry on an already very tasty sundae. The ball may already be slipping out of Boldin's hands when Howell makes contact, but the blur of white darting through Boldin's peripherals certainly affected his concentration on this particular catch.
By suffocating the 49ers receivers, it allowed the Colts pass rush a little extra time to get pressure on Colin Kaepernick. The Colts finished with three sacks and consistently made Kaepernick move awkwardly in the pocket. The defensive line's discipline in "cupping" Kaepernick and not giving him lanes to run was wildly successful and kept him from using his speed to punish the Colts for using man-to-man coverages (which often force secondaries to turn their backs on the quarterback).
Because that four-man front could get pressure, the Colts could afford to use a spy, which generally was Jerrell Freeman. Freeman played his role perfectly for most of the game and finished with a sack, forced fumble and numerous plays in which he forced Kaepernick to throw the ball away or end a run prematurely.
As the season goes on, the Colts may not face other teams that have quite as depleted receiving corps, but nevertheless, they have the talent to cover, and cover well. If they cover anywhere near as well as they did on Sunday, the Colts have the potential to slow any offense, save maybe the one in Denver (there's a limit to how many receivers you can cover, especially when the quarterback is, well, the best).
For more All-22 breakdown, check out Ben Savage's in-depth review of the All-22 film.