The Colts defense was bad last season. 

Run defense, pass defense, you name it, and the Colts probably were bad at it. 

The team finished 32nd in defensive DVOA against the run, 29th against the pass and 27th in adjusted sack rate. 

Well, through four weeks of the 2013 season, Indianapolis made dramatic improvements across the board, but one area in particular has stood out: the secondary. 

Yes, the Colts defense has played well against the run at times, but their DVOA against the run is still just 26th in the league. They've been able to rush the passer pretty well, but mainly through blitzing extra linebackers, not from improved base pass rush. 

No, the biggest reason for the Colts' defensive resurgence has been the improved secondary, which is playing as well as it can be right now.

Just before the season I wrote an article titled "Irrational Confidence: Making an Argument For and Against the Colts' Secondary." In the article, I discussed the optimistic things that the secondary had going for them, and then countered with the questions and negatives that came along with those same players. 

Well, four weeks into the season, and just about every one of the positives is coming true for Indianapolis, while few of the negatives are. The only pessimism that's been truly validated is questions about how LaRon Landry's health and Delano Howell's strong play have effectively balanced out Landry's absence. 

With everything going right, the Colts are currently sixth in the league in DVOA against the pass, a huge jump from where they were last season. Yes, that number is helped by the quarterbacks the Colts have faced, but it's still remarkable. 

So how exactly did they do it?

How did the Colts get here, and what are they doing that's proving so successful? 

Spend, Spend, Spend: It's Like Congress, Except it Actually Worked

To understand how the Colts shuffled and re-stocked the secondary, one has to start in 2012 with the controversial (although not in comparison to the Trent Richardson trade) trade for Vontae Davis.

While the Colts may not have gotten the highest value from their second-round pick, as they only keep Davis for two years before he has to be re-signed, he's still been a key part of the defense and was a big factor in the Colts' playoff run last season. 

Ryan Grigson wasn't afraid to pay a high price for defensive backs, and he shelled out $15 million over three years for Greg Toler, who was previously a role player in Arizona, before signing LaRon Landry to a four-year, $24 million dollar contract. The Colts would also re-sign Darius Butler during the 2013 offseason to a two-year, $4 million deal.

A second-round draft pick and $43 million later, the Colts had their starting secondary, with Antoine Bethea already on the roster.

While great teams are built in the draft, the Colts built their secondary through free agency and trades. This is beneficial in that they haven't needed as much adjusting as rookies might, but the downside is that there isn't much room for improvement in these players. 

For better or worse, the pieces were in place. 

Cornerbacks: No More Cushion, No More Zone (kind of)

For years in Indianapolis, the cornerbacks were taught to be conservative in coverage, not allowing the big play and putting an emphasis on tackling well.

While this strategy worked well at times (2005 and 2007), it did allow for elite quarterbacks and wide receivers to find holes in that zone coverage and exploit them. At times, that cushion was the hole in the zone. 

In 2013, however, the corners run a number of coverages, but are using press-man coverage more than any time in recent memory. 

This look has become commonplace in the Colts playbook, especially over the last two weeks. 

In looks like this, the Colts' assignments are often simple, man-to-man concepts, and the Colts cornerbacks have responded well, for the most part. 

But the Colts do mix things up, and one of the best plays in the Jacksonville game came on a different look for Indianapolis. 

At first, this 3rd-and-4 looks like a typical man-to-man assignment for Indianapolis. All three corners are matched up tight on the line of scrimmage, a logical play call with a short third down like this. But when the Jaguars motion, the Colts shift, and we can see different responsibilities play out for the corners. 

As the split-out receiver comes inside, Davis backs up behind Butler, who stays in the slot. The two now have different roles.

Rather than just adhering to tight man coverage, the two likely have some sort of pattern-matching responsibility here. Butler's first read is the receiver who's come in motion, while Davis' is the slot receiver.

But the roles are flexible: Butler is responsible for the short, outside zone (or flat), while Davis is responsible for whichever receiver runs a deeper route. 

It's not a straight zone or man coverage based on how the corners read the receivers and react. Meanwhile, Greg Toler is in a simple man-to-man responsibility on the other side of the field.

The slot receiver squeezes through the traffic and runs a crossing route. Davis takes a half-second to read the two receivers and then fully commits to his man. Butler reads the play-action and stays a yard or two back from the line of scrimmage in case that receiver breaks out into a route. 

Gabbert has three options on his roll out, but all three are well covered by the Colts. He chooses to go to the slot receiver (Jeremy Ebert), who has the best chance at separation. 

Fortunately for Indianapolis, Davis closes well after reading the play and is able to get both hands on the ball as he breaks up the play. 

The flexibility in coverages is extremely helpful for the Colts, and while the corners seemingly run much more man-to-man coverages, there are ways to camouflage and adapt those to make things harder on the offense.

The Safeties: The Linchpins of Everything Ever

While the corners and their tight man-to-man coverages have been important to the defense's improvement, the safeties and their versatility are arguably the most important key to Greg Manusky's defense. 

We've talked ad nauseum about two main roles the safeties have played over the last two weeks.

Generally, the Colts have played them single high, one safety falling back into a deep center-fielder role with the other creeping up into the box. The Colts use both safeties in this role, and you can see that in the two examples above. 

In the first, Delano Howell is near the line of scrimmage, and Bethea falls back in zone coverage. In the second play, Howell is the single-high safety while Bethea steps up.

Generally, the safety in the box is responsible for run support and man coverage on a tight end or running back (usually a tight end). In general, this has been very successful, especially with Delano Howell in the game during the last two weeks.

Bethea and Howell have combined to allow just 4 catches on 10 targets in 190 combined snaps in coverage. Two of those came in the fourth quarter when the Colts were already up 20+ and were playing to prevent defenses. 

Bethea and Howell currently rank 4th and 22nd among 85 qualifying safeties in coverage snaps per reception allowed, according to Pro Football Focus (subscription required). 

The two have picked their spots well over the past two weeks, being aggressive in key spots to get stops without allowing big plays. 

You can find examples of this against the run: 

As well as against the pass: 

When there's not a tight end to play man coverage on, the Colts often stack a safety over the opposing team's best receiver, like they do here with Delano Howell over Cecil Shorts on the far side. 

You can see that Howell isn't feigning interest in the middle of the field at all and is simply providing support over the top for Davis, which he needed on this play, one of the few where he was beat on the day. 

This method was effective against Anquan Boldin and San Francisco in Week 3 as well. 

Man-to-Man: I Spy With My Little Eye... A Domino Effect

Man coverage is great if you have the players to do it, but it does have one important side effect.

With the members of the secondary turning and running, they turn their back from the quarterback, giving big opportunities for gains on the ground by a mobile quarterback or even a little draw play to a running back. 

The Colts, however, have been able to counteract for the last two weeks with a spy.

With the safeties often taking care of the tight ends or running backs in the passing game, there is usually a free inside linebacker (Jerrell Freeman, most of the time). Instead of blitzing him incessantly (there is blitzing that happens, but usually at least one ILB hangs back), the Colts assign him to sit back about a yard or two back from the line of scrimmage and spy the quarterback. 

This has allowed the Colts to keep guys like Colin Kaepernick contained in the pocket, while also protecting against delayed draws or running back screens that net big gains. This isn't always an inside linebacker, the Colts have used outside linebackers like Erik Walden and safeties like Bethea in this role at times as well. 

No matter who it is, the Colts have been successful with the method, notching multiple sacks over the last two weeks from the spy, as well as foiling scrambles before they gain more than a yard or two. 

For example, the Colts were able to recover a Kaepernick fumble that came on a Freeman spy play. As Freeman waited for Kaepernick to tuck the ball, he cut him off before he was able to escape the pocket. 

In Conclusion: So Far, So Good

The strong play of the secondary for the last two weeks has made an impact all over the field.

We've already discussed the spy. The press coverage has also helped mask the lack of quick pressure from the Colts' defensive line. The Colts' pass rush isn't terrible, but it's not particularly fast either. Not allowing a cushion has kept opposing offenses from racking up easy yards and avoiding the pass rush with quick slants and curls. 

Can the secondary continue this level of play? That remains to be seen. 

The 49ers and Jaguars receiving corps are some of the worst in the league, so that has certainly helped Indianapolis. The next four weeks will tell us a lot about the secondary's true potential for this season, with Seattle's deep group up first in Week 5. 

Regardless, the results through the first quarter of the season are overwhelmingly positive.

Are they perfect? No.

Ryan Tannehill, for example, had his best game of the season against the Colts. 

But overall, early returns on the investment in the secondary are notable for Indianapolis, which, considering the money it took to build, is a good sign.