My DS2 (my DS1 is mine, not both of ours) went to stay with ex-DH (his Dad) and his stepmum (she's been around for 7 or 8 years) DS2 is 11.
Stepmum made an innocent but hurtful remark re "chubby cheeks" (DS2 is a tiny bit chubby) and he sulked. He continued to sulk and was a bit sulky and rude to stepmum.
DS2 has a statement of SEN and doesn't always "get it" and stepmum is a nice woman with kids of her own who has known him a long tim, since he was v young.
Anyway, ex-DH reacted angrily and squeezed DS2's leg so hard that he left a hand shaped bruise.
DS2 is so sweet and so well meaning that he would only have been embarrassed at the "chubby cheeks" remark and would have come out of it given time.
I have never, ever raised a hand to him, he is not that kind of kid. You just have to explain what has gone on and he wants to help.
I am livid at his father for bruising him and have asked him to apologise to DS2. He says, "No way, he was rude". DS2 says he never wants to see his father again.