3rd down back
Mewelde Moore is often described as a 3rd down back.
What is meant by a 3rd down back?
I think what`s confusing is that the term implies that a 3rd down is a standard measurement or play when surely it could, for example, be 3rd and 1 or 3rd and 20.
Would not a different play be used In each scenario?
Thanks for any help with this.