The words legal and revenge don't coexist. Remember that even under Human Judicial System, one cannot be both judge and party. When one person decides to act in revenge, they undermine the existing Judicial System and its Laws, whether Human Justice or Divine Justice. In so doing, they self-proclaimed as the best judge for the case and condemn the other party as guilty. Ethically or morally, that doesn't sound right, and it is simply not legal.
The bottom line is that, everyone is fully responsible for their own actions. You will always bare full responsibility for all your deeds including your reactions. We can find all possible reasons to humanly justify how we act, but the Divine Laws are immutable “What a man sows, he shall reap”.
Imagine a scenario where the perpetrator feels like your Justice (revenge) is not proportional or fair. If you give yourself the right to self-justice (revenge) then, they too, have the right to re-revenge, so where does it stop?
This is the part of life that will test whether a not a human has grown to maturity. If someone does wrong to you and you are certain of your own innocence, why waste time complaining? If you complain when you are innocent, then what would you do when you are guilty?
If you are a believer of Karmic Law like some of us, meaning that everything that happens to us in this life can’t only be exclusively attributed to the happenings of this lifetime alone, what if in your previous life you were 10-times crueler to that person and/or others? Life is also a school, a place for each one of us to learn through experiences with the goal of overcoming our weaknesses. Self-control is a quality, not a weekness.
My point is that revenge is worthless. But just as with everything in life, you have your own free will to decide and chose your course of action, but the Divine and Living Laws always have the final say in terms of punishments or rewards.