It's not uncommon to have a sport specific person in some capacity below the AD.
As an example, Thad Matta is the assistant AD over basketball at Indiana. His role is not to tell the head coach what to do despite having been a successful head coach himself. Matta is there to only worry about basketball, whereas the AD has a lot more on his plate. Matta makes sure the basketball program has what it needs, and if it does not, will go to the AD to get the basketball team what it needs.
I'm confident Bama and OSU have someone in a similar role for football. This is all part of the support staff arms race currently occurring in college sports.