Can 12/2 cable be exposed in a crawl space?
Yes a crawl space can have your 12/2 attached directly to the floor joists if going along the joist if going perpendicular a rat run is needed for smaller than 2 ea #6 or 3 ea #8 wires see exhibit 334.1 in the code , nmb in this location has been code for decades. Rat run or 1/2” plywood minimum.
Note bored holes need no protection.