A little more insight: https://www.ajc.com/blog/atlanta-falcons/closer-look-keith-armstrong-candidacy/tGPYyWww8ln1DcsSALniJP/
Armstrong’s units have consistently been ranked among the league’s top groups. He was one of the stars during the team’s appearance on HBO’s Hard Knocks. Perhaps, the Falcons could benefit from his man-to-man communication skills and he was put out front to help lead their "Toughness campaign."
https://www.revengeofthebirds.com/2018/1/6/16856890/arizona-cardinals-head-coach-keith-armstrong
”People get all hung up in these offensive and defensive coordinators, and special teams coordinators work with the entire team,” Arians explained. “So they have that presence and that connection with offense, defense, everybody. To me, it makes more sense. Plus, he’s had background in both offense and defense.
”He’s a leader of men,” Arians said. “He’s got grit, toughness. He’s a great family guy. His time will come, yes indeed.”