It's a significant step for the 21-year-old, third-round pick out of Louisiana State, who has come under much scrutiny because of off-field issues.
Thankfully, the news of out the Cardinals' OTAs is positive for Mathieu. He's been working with Arizona's first-team nickel package, according to NFL.com. Sports Illustrated's Peter King wrote that Mathieu has impressed the coaches at safety. So while people are impressed so far, the better question is what role should Mathieu play in the Arizona defense in 2013?
Thankfully, there are a few highlights that showcase his versatility as a defensive back. The highlights each run about 10 seconds and you may want to turn down the sound.
1. Mathieu could perform as a slot cornerback. Given his size (5'9", 180 pounds) he would match up better against the smaller slot receivers. There's little doubt he has the speed and vertical leap to keep up with receivers and make plays in the passing game. This is the most likely way he'll be on the field in 2013.
2. In passing situations, Mathieu could perform as a nickel back. With opponents like the New Orleans Saints and Atlanta Falcons on the schedule, Mathieu should get snaps and chase down receivers when those teams line up four-wide with empty backfields.
Notice the speed at which he closes on current Arizona teammate Ryan Swope to make this interception.
3. Mathieu's speed would make him an excellent spy from the defensive backfield. The Cardinals are going to take on some mobile quarterbacks this season, and using Mathieu to spy them might help minimize their effect. With Cam Newton, Michael Vick and Jake Locker on Arizona's schedule, plus two divisional confrontations each against San Francisco's Colin Kaepernick and Seattle's Russell Wilson, Mathieu might be able to make an impact.
With his size, he might not be able to tackle a bigger quarterback like Newton, but he could slow him down long enough for additional support to come. He could also take away running lanes, force quarterbacks to the outside and limit their gains. Arizona was torn up by the run last season, so any sort of help would be a boost to a defense that was 28th against the run, allowing 137 yards rushing per game.
4. Mathieu could perform as a blitzing defensive back. His speed makes him a problematic matchup for an offensive lineman trying to protect his quarterback. And what makes Mathieu dangerous in this role is his ability to force fumbles by chopping down on the quarterback's arm while coming off the edge. Arizona finished at a -1 on in turnovers in 2012, but that number should be on the positive side of the ledger this year.
That change will hopefully impact the scoreboard in Arizona's favor, too.
5. Mathieu could perform as a gunner on punt coverage. That kind of speed would be dangerous in the open field. He'd be able to close quickly on punt returners and reduce the Cardinals average yards per return allowed (8.6 in 2012.
As we see in these highlights, he also has a good ability to rip the ball away from returners and create turnovers.
6. Mathieu could perform as a punt returner. If Arizona puts him on the field with Patrick Peterson, opposing punters are going to have one safe option—kicking the ball out of bounds. With two Tigers back to return kicks, don't rule out reverses or fakes, which could draw defenses in the wrong direction and open lanes for whoever is returning the punt.
This last highlight shows him taking it to the house against Georgia.
Overall, Mathieu should play a prominent role in the Arizona defense in the coming season. It's hard to say right now how many of the six roles mentioned above he might wind up doing in any one game.
Fans should expect Mathieu to be involved in the defense and special teams units. Look for him to make a couple game-changing plays during the season. He'll force a few fumbles and pick up a couple sacks and interceptions along the way.