In a crawl space, can I staple the electric 12/2 cable to the floor joist?
Current Code has a certain rule for running non metallic and simlar cables in craw spaces.
334.15(C) 2017 NEC Cables not smaller than #6/2 or #8/3 can be directly stabled to the lower edges. Smaller cables can be run through bored holes or running boards.
The running board solution is usually the easiest. The running board should be at least the height of the cable.
In my jurisdiction, at least, I have received confirmation that this is acceptable.