I am adding a celing fan in a room in a condo that did not have any light fixture in it before. I have ran the wire from a wall switch to the fan box but have not used any conduit do I have to use conduit for the run in the crawl space also do I have to use conduit down to the wall switch box or can it just be run behind the drry wall.

Need to check local codes. For example, in Chicago area, everything must be in conduit.

If not needed by local codes, then cable should be fine.

Cannot just staple cable to the bottom of joists, need to staple to a running board.

Crawl spaces are usually considered "wet" and require sealed conduit or UF cable which is easier. MNC can be run without conduit in dry walls.