So we have this volunteer “grass” that sprouted from where we dump our straw outside the pasture. Wondering if anyone can tell me what it is. It seems really drought resistant, wondering if I can try grow it over some bare spots in my pasture.

Looks a bit like goose grass but the growth I see is a bit more upright. I also refer to goose grass as hard crabgrass as opposed to lime green soft crab. Just my terminology.
Never know what your getting with straw unless you can pick out of the field. If you can, it's easy to see what the predominate weeds are. If you don't see weeds in the field, find another source. No weeds = chemicals.

Thanks, I googled goose grass, and that’s one that we have here for sure, I actually dug a few out yesterday. So I don’t think this grass is that. It seems to stay pretty upright like you noticed