Like the other poster said, the teacher should've got up and left the room to alert someone with authority that could put their hands on her, or detain her if necessary. I'm not gonna stay seated there while she's trying to talk down to me/get in my face.
Also, if he really is just the substitute teacher, he don't even gotta worry about "looking weak" in front of the other students. He won't see them that often anyway.
Somebody should send this video to President Biden and see if he can make some moves to give teachers more power/control/authority over their classrooms. This teacher looked like him and Biden could be old friends.
I wonder what it's like in Russian and Chinese high schools (I mean, we have stereotypes of how strict it probably is, but I wonder what it actually looks like in 2021.)