Sometimes you need to run a circuit through both protected & unprotected space. For example, you might put a recep in workshop (unfinished walls = unprotected) over a crawlspace (protected).
To protect the wires in the unprotected space, you use a short length of EMT from the crawlspace, through the floor, to the junction box.
While people usually run separate THHN conductors through EMT, in this case it makes sense to use NM through the crawlspace and in to the EMT.
At the jbox, I'd normally use a NM clamp to hold the NM cable, or a set-screw connector to hold the EMT. What connector is appropriate for that end?
At the other end of the EMT, there is no box - just open space. What is the right fitting at that end?
EDIT: I think there are three goals here - clamp the NM cable in place, protect the cable from the sharp edge of the EMT, and secure the EMT to the jbox on one end.