consult parshat Pinchus.
The Weekly Parsha: A New Dimension
by Rabbi Heshy Grossman
Parshas Pinchus
THE ZEALOTRY OF PINCHAS
"....and the people began to commit adultery with the daughters of Moav. And they called the people to sacrifice to their Gods, and the people ate and bowed down to their Gods. And Yisrael joined himself to Ba'al Pe'or, and the anger of Hashem was kindled against Israel. And Hashem said to Moshe, take all the chiefs of the people and hang them up before Hashem, against the sun. And Moshe said to the judges of Yisrael, kill every one of the men who have attached themselves to Ba'al Pe'or. And one man of the B'nai Yisrael came, and brought to his brothers a Midianite, in the sight of Moshe, and in the sight of all the congregation of B'nai Yisrael, and they were weeping at the door of the Ohel Mo'ed.
And Pinchas, ben Elazar, ben Aharon HaKohen saw it, he rose up from among the congregation, and took a spear in his hand. And he went after the man of Yisrael into the tent, and stabbed both of them, the man of Yisrael, and the woman, through her belly. And the plague was stopped from the B'nai Yisrael. And those that died in the plague were twenty-four thousand.
And Hashem said to Moshe, saying. Pinchas ben Elazar ben Aharon HaKohen has turned my anger away from the B'nai Yisrael, in that he was zealous for My sake among them, and I did not consume the B'nai Yisrael in My jealousy. Therefore, say, I am giving to him my covenant of peace. And it will be his, and to his children after him, a covenant of eternal priesthood, because he was zealous for his G-d, and atoned for the B'nai Yisrael." (Bamidbar 25, 1-13)
The deed of Pinchas was one of zealotry, there was no Halachic imperative to kill Zimri, the Nasi of Shevet Shimon. In fact, were Zimri to turn and defend himself by killing Pinchas, he would be acting completely within his rights
Thank you. I was familiar with the bible story of Pinchas and Zimri although I never thought about applying the term generally.