This move makes sense on the surface.
Sherman did not fit the Cardinals' new offense, which does not utilize a traditional fullback. Arenas, a 2010 second-round choice by the Chiefs' previous leadership, projects as a slot cornerback in a division that has added slot receivers Percy Harvin and Tavon Austin.
"Size hurts him, but Arenas is feisty and a big-time asset on special teams," said Matt Williamson, who scouts the NFL for ESPN.com.
The Chiefs signed veteran corner Dunta Robinson before using a fifth-round choice for cornerback Sanders Commings. They added cornerback Sean Smith in free agency. They already had Brandon Flowers. Arenas was apparently the odd corner out.
The Cardinals plan for 2013 third-round choice Tyrann Mathieu to play weak safety and slot cornerback, but Arenas would come to Arizona with game experience. Mathieu and Arenas are both 5-foot-9. Arenas is listed at 197 pounds. Mathieu is listed at 186. There is overlap between the players. Arenas could also provide some insurance for Mathieu, whose off-field issues have made him a higher-risk player in the Cardinals' eyes.
Arenas started nine games last season and played 693 snaps on defense, the third-highest total among Chiefs defensive backs behind Eric Berry (967) and Flowers (840).