Diaz served apprenticeships under defensive minds like Mickey Andrews and Chuck Amato. He's energetic, wearing cleats on the field so he can run around and be near the action. He's highly quotable — once comparing safety Kenny Vaccaro to "a pack of rattlesnakes" and stating that offensive coordinator Bryan Harsin's motion-heavy offense has "tight ends coming out of helicopters and secret holes in the ground." He preaches both being fundamentally sound and the need to be aggressive.
But Diaz has another trait, one that separates him from many in his profession: he's a stat-hound, and somebody who stays on top of the latest advanced statistical metrics.
According to Diaz, the trend started when he became a graduate assistant at Florida State. Diaz attended school at the Tallahaase powerhouse, but didn't play football. And after graduating, he went to work in television, becoming a production assistant on "NFL Countdown." But Diaz had a desire find a place on another side of the game — as a coach — and he joined the FSU staff in 1998.
The Seminoles were at the height of their power, playing for two national championships, winning one, and going 23-2 during Diaz's two years there. And Diaz was at the bottom of the food chain, trying to find some way to make an impact.
"When I got to FSU, the defensive coaches that I was fortunate enough to learn under, they were on top of the game," Diaz said. "But there were some things in terms of breaking down our opponents that we weren't doing all the way yet.
"That was sort of how I could provide my niche," Diaz said. "I could ask 'hey, what about this' and offer things that way. Because they certainly didn't need any suggestions on how to coach defense because they were awesome at it."
At that point, many of the more advanced metrics that are used today, weren't in existence. And — just as today — many people judged defenses by the number of yards allowed, a stat called "total defense." But the problem with total defense is that it doesn't tell the total story, Diaz said.
"At N.C. State in '04, we led the nation in total defense and we won five games. So there had to be something more to it than yards allowed, because yards allowed can be very deceiving," Diaz said. "It's really kind of flawed."
Picture a team up by 20 points late in the game. That team is likely playing prevent defense, allowing the opponent to pick up easier yards by keeping the ball in front of the defense and limiting big plays. The other team racks up yards, hurting the winning team's total defense. And the opposite is also true: if a defense is the side behind by 20 points, the opponent runs the ball into the line, making for easier stops, and therefore a better total defense, even if it doesn't affect the game's outcome.
Then, there are the issues with sample size and scheduling.
"The problem with college football is it's actually the worst sport statistically because it's such a small sample size and then [you have] the wide disparity of conference games versus non-conference games," Diaz said. "The stats in terms of who finishes first in the country in total offense or total defense, a lot of that really has to do with scheduling."
If Diaz focused on new ways to break down the game during his time at Florida State, Michael Lewis's opus "Moneyball" served as the next trigger. In the book, Lewis trails the Oakland A's for the 2002 season, shedding light on how the baseball team was able exploit market inefficiencies — pressing statistical advantages and relying on cold, hard numbers — to make the playoffs despite one of the lowest payrolls in baseball.
Diaz read the book, recently made into a movie, during his time at N.C. State, and said he thought the book had applications to college football, especially in recruiting.
"The book was as much about player selection as it was game theory," Diaz said. "Football is such a unique sport, and high school football is an even smaller sample size and sees even more of a variance in who you're playing and whether you're recruiting a kid from the center of Houston versus a kid from upper Iowa, there could be vast differences.
"It's very hard to compare a quarterback who throws for 5,000 yards in Walla Walla, Wash., to one who throws for 4,000 yards in East Texas," Diaz said.
But beyond the micro level, Diaz said the coaches looked into talent hotbeds. For instance, while everyone knows that Texas, Florida, California and Ohio are huge producers of talent, largely because of the populations in those states, Mississippi has actually been one of the best per-capita producers of NFL Draft picks in recent history. And that's an advantage that Diaz said Bulldog coach Dan Mullen tapped into.
"Like any good farmer, you have to know what your fields can grow," Diaz said. "There were some really good players in Mississippi."
But statistics were also changing for in-game analysis. Whereas it might once be considered an advanced metric to look at red zone efficiency, Diaz said Texas is focused on red zone touchdown efficiency.
"You can win a national championship by making people kick field goals in the red zone," Diaz said. "And you can finish last, in theory, in red zone defense. It just doesn't make sense."
Diaz also pointed to the percentage of fumbles recovered. In 2010, the year before Diaz arrived in Austin, Mississippi State was in the top-three nationally in the statistic. Texas was in the bottom three nationally. The Bulldogs went 9-4, including a win over Michigan in the Gator Bowl. Texas went 5-7 and missed going bowling for the first time since 1997.
"It we had been flipped, our records might have been flipped," Diaz said. "It definitely gives you something to think about."
And that thought process no longer belonged just to coaches.
"I really think what's happened, that is fantastic, is taking smart people plus computers plus too much free time," Diaz said. "There are a lot of people doing outstanding work on the Internet.
"They're taking the play-by-plays and adding more than just what the normal stats put out there," Diaz said. "They're not always on the right track, but sometimes they are. And that's somewhat of a recent phenomenon."
That phenomenon has given rise to statistics like Slow Grind — the number of plays a defense forces an offense to take to score — and the FootballOutsiders.com S&P+ Ratings, a play-by-play success rate that factors for situation and competition.
Looking at the latter rating, you can see Diaz's 2011 Texas defense come to life through the numbers. The Longhorns finished No. 4 nationally in the statistic, but were especially good on running plays — a major Diaz focus — and on winning passing situations (defined as second down with eight or more yards to go, or third or fourth down with five or more yards to go). Texas was third nationally in Rushing S&P+, and second only to national champion Alabama in Passing Downs S&P+.
"Those are the tenets of our defense," said Diaz, who follows both S&P+ and Slow Grind. "We'll show those kinds of things to our players during the season just to reinforce what we already know. There aren't usually any 'eureka' moments, but it works more side-by-side with what we see on film."
And film is still necessary. Because while the numbers "have no emotions" according to Diaz, there still aren't great ways to gauge individual defensive performances.
Tackles and hurries are charted differently by different schools. A defensive lineman could get credit for a coverage sack, or a sack when another player chases the quarterback into him. And interceptions could be the result of a quarterback being pressured, or a bad pass, or great coverage on another player's part.
That's why Diaz said the film is important, and why players are coached to focus on their performance, rather than the play's outcome.
"Last year, everybody was wondering six games into the season why our defensive ends couldn't get sacks, and then the next couple games they started getting sacks," Diaz said. "But we were also covering better those games. Quarterbacks maybe held onto the ball a half-second longer. All of a sudden the defensive ends get the plaudits, but a lot of it was maybe because of the coverage.
"Nothing happens to a defensive player in a bubble," Diaz said. "That's what makes college football the opposite of baseball. Because in baseball, everything happens in a bubble: this guy pitches, this guy hits and the ball is hit to that guy."
Because of that, Diaz said it would be difficult to come up with accurate statistical measurements for individual defenders. But he said the fact that people are finding different ways to look at the game was a great thing.
"The way an iceberg looks from a ship going by is very different from what's happening beneath the surface," Diaz said. "That's what's so fun about this game. There's so much going on beneath the surface, and I think that's the point.
"People are starting to not just accept the vague, broad analysis that they get from their local paper or whoever's yelling at them on ESPN," Diaz said. "They can say ' gosh, I can look at a box score. I watched the game just the same as the guy in the press box. Maybe I have something to add, too.'"