Ignoring morals and ethics and focusing mostly on historic precedent?
Firebombing a few city blocks. Possibly letting the angry young soldiers run wild on the civilian populace under the guise of getting “justice” for the civilians that hamas brutalized.
That is more or less “war”. You raid one of my towns, I’ll raid two of yours. Ends when one side has been beaten into submission.
Actively attacking third party civilians is not. The IDF has a very long history of doing this.