The pacifist believes that one ought not engage in problematic violence in war even if all the standard jus ad bellum conditions are satisfied. "Problematic violence" here means the level of violence that is prohibited. Probably few pacifists would think it would be wrong to push violent foreign soldiers away without hurting them. So, presumably, pushing someone painlessly away doesn't rise to the level of "problematic violence." Where the pacifist draws the line may differ from pacifist to pacifist, but I take it that lethal violence, i.e., violence that, if successful, has a high probability of resulting in the opponent's death, counts as problematic, even when the death is not intended. Thus, I take it that the pacifist will be opposed to shooting at an enemy soldier's heart even when one is using double effect and intending the disablement rather than the death of the enemy soldier. This is all stipulative of what I mean by "pacifist".
Question: Can the pacifist consistently permit problematic violence in law enforcement situations?
If not, then pacifism is seriously problematic, since it seems pretty clear that it is practically impossible to have a decent, self-sufficient community enduring over time without lethal violence to contain violent criminals.
But I think the answer to the question is in fact negative. For how could one draw a line between war and law enforcement? When the invading army marches in, burning crops and murdering citizens, they are breaking the victim country's laws. If problematic violence is permitted to enforce the laws of one's territory, it should be permissible to use problematic violence to stop them. But this seems to be a case of war. Hence, some lethal violence is permitted in some wars, contrary to what I stipulated as the view of the pacifist.
Perhaps, though, the pacifist could claim that it is only permissible to enforce a country's laws with problematic violence on the country's subjects, and an invading army does not consist of subjects. But this is deeply implausible. If it is permissible to use problematic violence to stop a citizen wife from murdering her citizen husband, it should also be permissible to use problematic violence to stop a non-citizen woman who sneaked into one's country to murder her citizen husband. Moreover, this should be permissible even if the woman was commissioned by another state to kill her husband. But if we allow that it is permissible to use problematic violence against criminals acting on behalf of foreign states, then there seems to be no way to deny that it is permissible to use problematic violence to stop invaders.
There is, though, a consistent position the someone could hold here: Problematic violence by agents of a state must be confined to that state's territory. This is not a pacifist position by my stipulation of what a "pacifist" is. But it may be thought to be a pacifist position in a broader sense. But I am not so sure. It seems that this is not so much a position against violence, as a position about jurisdiction.