The Cardinals were looking for linebackers during the preseason. They ended up finding one in the secondary.
To be truthful, as soon as the Cards brought in Zeke Turner, they had that thought. He was officially brought in as a safety, but the Cards saw him as a (Pac-12-from-a-Washington-college) guy who could move up and play in the front seven. Just like Deone Bucannon. Turner was officially listed as a safety all through camp and the preseason, and truth be told, the transition figured to take a while. But then Turner was out in the last preseason game playing almost exclusively linebacker. Then as the Cardinals put out their first roster of the 53-man variety, Turner was listed as a linebacker.
How the Cards approach defense -- and their linebackers -- will be an evolving storyline. The Cardinals weren't going to unveil too much in the preseason, but it was noticeable that in both the last two games, they went almost exclusively nickel on defense. It meant that Bucannon and, somewhat surprisingly, Josh Bynes, were the two linebackers playing with the first unit in Dallas. Haason Reddick was playing with the second unit alongside Gerald Hodges.
Meanwhile, Turner was the guy playing the Bucannon/Reddick role in the final preseason game. (And, if you thought of him as a safety, it meant a defense with six defensive backs most of the time.) Turner is still a rookie, and still learning, and as long as Bucannon and Reddick avoid injuries, he won't be needed on defense. But he's a good story as most undrafted rookies are. The Cardinals certainly wouldn't frown if they could develop another Buc.