INDIANAPOLIS -- Matt Eberflus could have been looked at as the outsider on Frank Reich's Indianapolis Colts staff last winter.

Eberflus left the Dallas Cowboys where he had spent the previous seven seasons, packed up his family and moved to Indianapolis where he was under the impression he would be part of Josh McDaniels' staff.

We all know what happened with that. McDaniels reneged on his verbal agreement with general manager Chris Ballard and returned to New England.

Ballard, a prideful person, kept his word to Eberflus (and defensive line coach Mike Phair and offensive line coach Dave DeGuglilemo) by still making him the team's defensive coordinator even though he had no prior relationship with Reich.

Ballard's decision to keep Eberflus has been one of the best moves he's made, because his defensive coordinator has turned what had been a porous unit into a ball-hawking group that has been one of the most underrated defenses in the NFL this season.

The Colts have the NFL's leading tackler in rookie linebacker Darius Leonard, they have forced at least one turnover in each of the first 12 games and the unit ranks 11th in overall defense.

That's a stark contrast to when the Colts finished 20th or worse, including 30th last season, in five of Chuck Pagano's seasons that featured two different defensive coordinators.

Eberflus will face his former team on Sunday when Dallas, which has won five straight, comes to Indianapolis to face the Colts (7-6), who are trying to stay in playoff contention.

"Chris' endorsement was really strong," Reich said. "Just having a lot of ties to that system when Chris was in Chicago, so Chris was very persuasive and very strong in his conviction that Matt was the right guy. It really couldn't have worked out any better. I know it's crazy. It's really an odd way for it to come together, but it literally couldn't have come together any better.

"Personally, Matt, I just have a lot of respect for him. [His] high character and integrity as a person -- just stands for everything that we would want -- carries himself the way we would want a coach to carry himself."

The relationship between Eberflus and Reich has been a relatively smooth one because according to the defensive coordinator, the head coach is "trusting in terms of who he is character-wise and integrity." Reich attends the defensive meetings to talk about the game plan and give his perspective from an offensive standpoint, but he's given Eberflus the freedom to run the unit.

The defense wasn't an easy fix for Eberflus, because for so many years it was the Colts' obvious weak link. There were numerous times when the offense needed to put up 30-plus points to have a chance to win.

"For him he was more focused on the now, not what happened in the past ... we're going to watch this system and how it has worked in the past and we're going to go from there," linebacker Anthony Walker said. "That's what we did. We're trying to live up to that, but also leave our own legacy in a system that has been around for 25 years."

The very first thing Eberflus did was scrap the previous regime's 3-4 defense and switch to a 4-3 Cover 2 zone defense while putting a premium on speed, speed and more speed with a starting unit that features six first- or second-year players.

His message to his group in one of their initial conversations was: Their defense isn't for everybody and they would be exposed in it.

"Meaning you'll be exposed in a good way or a bad way," Eberflus said. "If you're coaching the right way and doing the right stuff, guess what? Everything is going to rise. It's going to rise where it's supposed to rise. The good players we have on our defense. All the guys that buy in to the fundamentals and are coached correctly all rise up ... Everything is out on the table. There's no hiding in the system. Can't hide the effort, can't hide the execution. The players know that. We tell them. The system hardens you to play a certain way and then what happens is, when guys buy into that, then it becomes a style they hold each other to."

The next thing Eberflus did was repeat over and over that they were going to aggressively try to strip the ball on every play. That has created a win-win situation for the Colts, because they have forced turnovers and given the offense a short field to work with. After forcing 20 turnovers last season, they already have 21 this season (tied for eighth most in the NFL) with three games remaining.

"He's always talking about it," Leonard said. "You don't know anybody who wants to keep getting hit in the face over and over again. If we keep going after the ball over and over again, at some point they're going to spit the bit and the ball is going to be out for us to get it."

The Colts held the Jaguars to six points and just 211 total yards in Week 13. That usually is good enough for a win, but not that afternoon because they lost, 6-0. Scores like that didn't happen often in the past.

Eberflus is one who is rarely satisfied. That's a good thing because he wants as much perfection as possible. He's been known to blow the whistle if a defensive lineman is lined up in the wrong position by a matter of inches, because if he can't do it right in practice, he's not going to do it correctly during the game.

It's all part of him not wanting his defense to be "exposed."

"He's probably one of the most detailed people I've been around," Leonard said. "He's very specific about every little thing. He's very passionate about the defense and always talks about the system, and he just tries to make sure everybody knows what they're doing and ... what everybody else is doing. It's things like that, that have allowed us to have success."