Loving my neighbour's enemy

The New Testament is _very_ clear that Christians should love their enemy and turn the other cheek. Similarly, Christians should defend others and stand up against injustice. These things are _somewhat_ at odds. An idealised Christian behaviour would be to accept mistreatment of _oneself_ over harming their enemy, and easily forgiving grievances. But what about harming "the enemy" who is mistreating someone else? As far as the end result is concerned, should a Christian harm "the enemy" attacking some other "innocent party", so as to protect the weak, or stand by, out of love for the "enemy"? Should the Christian do the minimal harm to the enemy that pushes against the immediate danger to the "third party", or go further than that, seeking more long-term security to the "third party"? Should a "Christian defender" easily forgive crimes committed against the third party out of love to "the enemy", or pursue them to correct the injustice, in favour of the "third party", causing harm to "the enemy"? Defending "the innocent party", or more broadly pursuing justice, may require doing a lot of harm to "the enemy" (think, for example, in the cases of armed robbery, or intervention in an unjust war), how should a Christian balance these responsibilities? I'm most interested in a Catholic perspective, but any Christian perspective is most welcome!