Exactly. The invocation, even in such a case (where one is facing police assault), is still not a “categorical imperative”, but continues to be a tactical calculation. Gandhi advocated violence in self-defence over becoming a victim (one, but not the only case he outlined is rape). But faced with an array of well armed police there are likely few circumstances(*), it seems to me, in which violence will either advance the cause or protect oneself (or others). Violence in such circumstances seems to be well-described by what Carrol wrote, an act of elevating violence to a principle. Tactics here apply to both to the immediate need of self-defence and the larger goal of winning support and obtaining sought after results.
In all of the above, I do not mean to muddy the distinction that has been drawn (correctly, IMHO) between property damage and violence to people (even while acknowledging Jordan’s post which questions the distinction between physical harm and material harm) i.e., I continue to be ambivalent about the BB actions, but I see some of the arguments of the side “defending” them.
—ravi
(*) Issues of complexity might make it difficult to calculate ad hoc real-time the success or fallout of violent action. So, one might use a provisional principle that unless there is a threat to life, violence should be avoided. But still, not a categorical imperative.