"When AD is singled up on an O-lineman . . ."
When AD is blocked by a single OL, the odds are he's going to cause trouble.
If you read between the lines of the comments of AD and some of his coaches/fellow players, you get the feeling
at least some of the reason he decided to retire was he was tired of facing 2B and even 3B teams.
It was frustrating for him.
And now
a (big?) part of the reason he's coming back is he knows with Garrett, Kobie, BY, etc rushing the QB with him, he's going to face
many more man vs. man opportunities. And he knows when that happens, he causes trouble and has a lot of fun and the D dominates.