As good as Kansas City's offense was, the team's defense was equally as bad. The Chiefs ranked 31st in total defense, and since 2013, no team entering the postseason had given up more points per game than the Chiefs (26.3). Two days after K.C. lost to the New England Patriots 37-31 in overtime of the AFC Championship Game, defensive coordinator Bob Sutton was relieved of his duties after six seasons.
The Chiefs hired Steve Spagnuolo, who during a 2018 away from coaching coincidently spent some time in Kansas City exchanging tricks of the trade with Sutton and had no idea he would be replacing him at season's end. During Spagnuolo's first week with his new players in K.C., he presented some daunting figures. He showed them the statistics of first-year defensive coordinators who came in and changed the scheme -- and the numbers were "just bad," as one player told me. But the players in that room bought into a strategic overhaul. They had no choice. They knew they were playing opposite one of the most explosive offenses this league has ever seen. And they knew that, after standing on the doorstep of a Super Bowl appearance in the 2018 campaign, not punching a ticket to Miami this season would most likely mean they were to blame.
"Back in the spring, we didn't know who to cover," Mathieu told me last week. "It was ugly sometimes."
It might not have been pretty, but what Spagnuolo did was take his time with actually teaching his scheme. He also understood it was going to take exactly that -- time -- to get his group to where he envisioned it could be.
"The coaches have done a really good job of taking their time with us and hit every detail," Mathieu said. "That's why I think a lot of dudes like playing for Spags, because they can see that in him. He didn't just jump into it. He really took his time with us and really taught us his defense."
Mathieu has been instrumental in the unit's growth. Spagnuolo told general manager Brett Veach shortly after he took the job that the free-agent safety was the guy he wanted to be the leader of his defense, and Veach made it happen. Mathieu came in and took over the locker room with his "innate ability to lead," as Andy Reid puts it.
Mathieu is also a chess piece. It was made clear when he signed with the Chiefs in free agency that Mathieu would come in and not just play safety, but line up at nickel corner and cornerback, blitz the quarterback and do everything in between.
"Way back when we installed in the OTAs, I remember putting up play sheets of certain coverages, not all of them, and I told them that as I explained what each person does, everybody should listen, because at some point, most of you will have to play a different spot," Spagnuolo said during the week before the regular-season finale against the Chargers. "I think when you can do that, it gives you flexibility, and maybe it gives the quarterback something to think about."
The Chiefs' defense struggled through the first six weeks of the season. They ranked 27th overall, 19th in scoring and 30th against the run. Mathieu had yet to be used in the fashion that was intended and was almost exclusively playing safety.
But all season, as Spagnuolo kept teaching, he also kept testing his unit on the practice field against some of the best offensive weapons in the game.
"We've been doing that all year in seven-on-seven," Mathieu told me of going against Mahomes in practice. "Pat will come in and give that look for the show team. And he be slicing and dicing. This is the first place I've been it's been done like that. I can always hear Spags saying, 'We need speed. We need speed. We need to see the looks.' I feel like Pat and Tyreek Hill ... First of all, [Hill is] the best scout-team receiver (of) all time."
Week 7 -- during Thursday Night Football in Denver, with Kansas City fresh off back-to-back losses -- is when the Chiefs defenders began to feel like they were finally starting to put it together. But given Denver's struggles early in the season, they didn't want to give themselves too much credit for holding the Broncos to just six points.
Over the next three weeks, Kansas City gave up nearly 30 points per game. But when Week 11 came, everything changed permanently.
"We started feeling it," Mathieu told me of the 24-17 win over the Chargers. "That Mexico game, I remember talking to Frank (Clark) specifically. Him and Chris Jones specifically. And those guys, the look in their eyes. They were tired of what people were saying about us defensively and it was like they were ready. Ready to just start dominating and they have been."
Since Week 11, the Chiefs have yielded just 11.5 points per game, a spectacular decrease from the 23.9 points per game they gave up through the first 10 weeks of the season. Teams ran all over Kansas City through those first 10 outings, to the tune of 148.1 yards per game. But ever since the mindset transformed during their trip south of the border, the Chiefs have allowed just 95 yards a game on the ground.
"I think our mentality just changed," Mathieu said. "Whoever is on the edge, set the edge. If you're a linebacker, play downhill. If you're in the secondary it's about mindset. You have to want to tackle. We just kept crushing it. And crushing it. And crushing it. And a lot of the huge runs we gave up, wasn't really knowing the scheme or trusting the scheme. I mean, Frank Clark has never played on a bad run defense. He doesn't know what that feels like and he took that personally."
Also, Mathieu started being used in the capacity that was originally planned, and he's not the only player being moved around playing different positions. Cornerback Kendall Fuller, who Reid believes will be a coach some day because of his football IQ, has been playing safety at times. Fuller has changed positions post-snap with Mathieu to confuse quarterbacks -- another wrinkle that was taught to both players in the spring, but wasn't really used in the first half of the season.
"The one good thing about the guys that we have back there in the secondary is that they can play dual positions," Spagnuolo said. "Listen, you have to know your personnel. You have to have guys that are cerebral. From the chin to the hairline, they respect it and work at it. Otherwise, you're probably hurting yourself if you move guys around. We'd like to be able to do that."
It appears Spagnuolo has a grasp of his players -- and they, in turn, appear to have the mental ability to execute the scheme. This is key, because in the wake of stud rookie safety Juan Thornhilltearing his ACL in Week 17, Spagnuolo will have to get even more creative with his defensive backfield in the postseason.
The Chiefs head into the playoffs with a first-round bye, just as they did a year ago. But the difference is they're heading into the postseason giving up a full touchdown less per game and have no intention of letting off the gas. The unit that was 19th in scoring defense through the first 10 games finished the regular season at No. 7. The plan was to have Mahomes and company go against the first-team defense again during the bye this week.
Something tells me there might be just a little less slicing and dicing this week from Mahomes. And without a game to prepare for, maybe Spagnuolo will have time to pull out those stat sheets from the spring and take a look at how they measure up to those teams of the past. But that's not why he was brought in or what they were looking to accomplish. So maybe pulling them out on the plane to Miami might be a more appropriate time. Spagnuolo has proven he has the patience to wait.