Mathieu, the absolute definition of a ballhawk, was dismissed from LSU before 2012, missed the entire season and reportedly failed nearly a dozen drug tests. But he spent his time away from football rehabbing his personal life (and his image) and appears to be paying immediate dividends for Keim's Cardinals team.
Keim called Mathieu's offseason thus far "outstanding" and praised the rookie's level of "commitment to the game" thus far.
"The thing that I didn't know for sure when we drafted him is what his commitment to the game is like in terms of preparation," Keim said. "He's a gym rat. He was one of the rookies that was first in the weight room every morning."
Keim also said that Mathieu, who still has to prove himself off the field, has inspired "a great deal of confidence" in his future at this point.
"He's obviously got a chip on his shoulder," Keim said. "Now we'll see whether he toes the line off the field, but so far, everything we've seen gives me a great deal of confidence that he's going to the do right things."
The Honey Badger -- Mathieu laughed that he couldn't ditch his infamous moniker -- has to be helped immensely by the presence of Patrick Peterson, his former teammate at LSU and de facto football mentor. Or maybe he's just grown up. Whatever the case, he's drawing positive press from his teammates too; quarterback Carson Palmer praised Mathieu's ability to find the football.
"Tyrann is getting his hands on a lot of balls," Palmer said Friday. "He's so quick and explosive in and out of breaks and reading concepts and knowing coverages and weaknesses in where we're trying to throw the ball."
Of course, Mathieu also acknowledged that he got beat by Peterson when the Pro Bowl cornerback lined up on offense (which, well, wow, that's impressive). And it's possible that a lot of this is the hyperbole that comes with training camp and offseason optimism.
But to hear what scouts and coaches told ArizonaSports.com's Ron Wolfley, well, it's hard to just ignore.
Wolfley writes that a scout called Mathieu "pound-for-pound, the best player on the field" at Cardinals training camp. And an offensive assistant coach told Wolfley that "No. 32 was going to change the team."
Given the talent on defense for Arizona, that's high praise. If Mathieu can justify the hype -- and play for Arizona in a manner resembling anything close to what he did at LSU -- he's going to end up being a steal for Keim.