Interesting call, due to the lack of displayed weaponry by the thieves. This is much more of a state-by-state question than a general, because it's protection of business property, not of home property or people.
I'd allow it, based upon a combination of FAFO and the guy hopping the counter which closes the range and increases the danger (as he, more than the clerk, found out) but, since this is not the old west era were FAFO was pretty much all you needed, I concede the legitimacy of calling it either way.