I don't think there is a specific list of what constitutes grievous bodily harm, I think it comes down to the facts of the event. As for me, I take it as anything that could cause a serious wound (gun, sword, knife, spear, cleaver, axe, etc.), anything that could cause serious head trauma (cinder block, brick, bat, club, hammer, etc.), anything that could cause severe burns (gasoline, acid, scalding hot liquids, etc.) or anything that could cause an immediate or near-immediate incapacitation that would leave me unable to defend against further attack (broken limbs or being struck by a MV for example). Any of those don't necessarily mean a threat of death, but certainly could result in death or a serious, life-altering injury. Things like age difference of attacker to defender and disparity of force (gang attack versus 1:1) certainly come into play, but I don't think they're automatic. I don't think being surrounded by 5 9-yr-olds would cut it but 5 gang bangers carrying an assortment of knives, clubs, or more definitely would cross the line. Gangs travel in packs just for the intimidation factor, so I don't think it's unreasonable to figure they aren't selling girl scout cookies but are a danger and act on it. YMMV.