That doesn't really apply in this situation. Both, Sami is definitely not in the wrong and this sends the wrong message, and also because IF (since the dad doesn't know) Sami is telling the truth, it basically gives encouragement to bully kid to continue.
Even ignoring that he doesn't side with his own daughter in a he said she said situation, dad's an asshole for just ending the conversation with Sami and ignoring her to take a call. Then later is all, hey get back here we're not done talking. 🙄
+a moron for saying there's no way hurting somebody is ok, in a self defense scenario, which Sami claims it is, it's obviously justified
Sami was standing up for a friend that was being bullied, and she was right for that. We don't know if she actually did anything or not, the author kind of intentionally left it vague (and maybe it doesn't even matter for the larger conversation). Kids at that age can be very focused on "right" and "wrong", but what's "good" and what's "bad" are going to be culturally influenced. American culture I think, by and large, would say standing up for yourself (and especially for others) is good. My mom's a foreigner, and she taught me absolutely the same thing. But that's not to say it's the same in Japan.
And, I think, part of the problem is that they never got to have a proper conversation about it. I don't want to resort to culture for every excuse, so let's just say yeah, he should've talked to Sami initially at school, instead of taking the call. And then later, Sami is mad (for good reason) and with Nishi butting in, we don't get a proper conversation where we can see any kind of reasoning or context. To me, this is a series about a single father who makes mistakes, we've seen that with like how he didn't recognize that she was putting on a brave face to try and make it easier for him. Not to say that it is what I said (i.e. feeling like you're right, but just deciding to pretend like you agree to get it over with), but it may be that he's viewing things through a more 'adult' lens, whereas she's viewing it through a 'kid' lens (and also has all the info, lol), and that's where we're getting a disconnect.
Considering the scrape is on the front of Kirara's knee, she probably just tried to move forward to do something, and tripped. I can kind of understand dad's concern, because Sami does have a whole other demon personality, but I think she's aware of what's happening during it. So I just want to end on, as somebody who works with elementary kids, they ABSOLUTELY lie and exaggerate, especiallyyyy if it's to cover themselves. And the parents who baselessly believe them and come to us demanding stuff, especially when their kid was actually in the wrong, aren't people to be praised either.